He's the son of Tsuyoshi Yamamoto, who owns a sushi shop named TakeSushi. It is left unknown what happened to his mother who is never seen or mentioned throughout the series. Takeshi grew up in Namimori and at some point, developed an interest in baseball; his love for the sport extended to the fact that he wore a baseball uniform in many of his childhood pictures.
In the manga, Takeshi asked Tsunayoshi Sawada for advice because he was worried about his baseball abilities getting worse, and ended up breaking his arm because he took it. He thought his career in baseball was the only thing he was good at, and planned to end his life. He was just about to jump from the roof top of Namimori Middle School when Tsuna came into the scene. Tsuna convinced him that he had much more potential, and then tried to run away, but Takeshi grabbed him, causing the two of them to fall off the roof. Their lives has been saved because Reborn shot Tsuna with the Dying Will Bullet, and he performed a "Mid-Air Reborn." In the anime, however the two became friends through a volleyball match.
During the Kokuyo Junior High Gang's attacks, Takeshi was ranked second strongest in Namimori Middle. When Chikusa Kakimoto attacked Hayato Gokudera, Tsuna and Takeshi came to his aid, leading to Chikusa's retreat. Later, Takeshi joined the group in the attack on the Kokuyo Gang and was ambushed by Ken Joshima, causing the two to end up trapped underground. Disadvantaged due to both his broken bat and Ken's ability to smell him, Takeshi was unwilling to be hurt because this was right before an important baseball match; however, once Tsuna was in danger, he sacrificed his arm to beat Ken. Later when Lancia attacked the group, Takeshi was able to figure out the secret to his chain ball attack but was overpowered nonetheless and knocked unconscious.
A month later, Takeshi, along with Gokudera and Tsuna, were defeated by the Varia henchman Superbia Squalo, who was chasing the Vongola messenger Basil. Later, Takeshi was chosen as the Vongola Rain Guardian and was given a half Vongola Ring. He then asked for sword training from his father in preparation for the Varia's arrival. His father scorned him for treating it like a game but still taught him the eight forms of the deadly Shigure Soen Ryu. Later in the week, Ryohei Sasagawa, Takeshi, and Gokudera defended Lambo from the Levi Lightning Squad. In the Rain Ring Battle Takeshi was set to fight Squalo again. Before the fight, Takeshi was warned by Dino that Squalo may have already defeated the Shigure Soen Style, though Takeshi remained determined to use it. Squalo did indeed know the style and used it against Takeshi. In the end, however, Takeshi won by creating his own technique in the middle of the battle. A shark was then let loose as part of the match, and, although Takeshi tried to save him, Squalo was pulled into the water. During the Sky Ring Battle, Takeshi was cured of the poison by Kyoya Hibari. Takeshi devised a cunning plan to rescue Chrome Dokuro but it backfired when they were caught in Mammon's illusions and were ultimately saved by Ryohei. Later the Vongola Guardians forced the remaining Varia to surrender and Takeshi was relieved to hear that Squalo had been saved by Dino.
In the Future, Takeshi led Tsuna and Gokudera to the Vongola Base where they met with Reborn who revealed that Takeshi's dad was killed by the Millefiore Famiglia. Later while searching for the other Guardian's Takeshi, Tsuna and Gokudera found adult I-Pin, Lambo and Haru Miura and Kyoko Sasagawa being attacked by Millefiore members, Nosaru and Tazaru, however before he could fight them Takeshi was swapped with his past self. After having the future situation explained, Takeshi (along with Tsuna and Gokudera) was taught how to use Box Weapons by Lal Mirch. Takeshi later went to follow up a lead at Namimori Shrine with Gokudera. They then encountered Gamma who Gokudera initially took on alone refusing to cooperate with Takeshi and was easily overpowered. However even when they worked together, Gamma's experience far outmatched them both. The two were then saved by the adult Hibari. After he recovered, Takeshi began training with Reborn who also gave Takeshi a DVD made by Squalo, titled 'The Road to becoming the Swords Emperor' which included 100 battles that Squalo won. After developing new techniques from the video Takeshi was successfully able to slice Reborn's hat. Reborn then told Takeshi about the secret of the Arcobaleno, but asked him not to tell anyone else until after they defeated the Millefiore.
Takeshi joined the others for the invasion of the Merone Base. Takeshi, along with Lal (who had been knocked unconscious during a fight), were separated from the others. Takeshi then encountered Genkishi who he recognized from Squalo's video. Despite making him draw his sword, Takeshi was overpowered by Genkishi's Illusions. After he was knocked out he was once again saved by Hibari. Later Takeshi along with the other Guardians was given a Vongola Box.
When returning to the past for the Arcobaleno Trials, Takeshi was chosen, along with Tsuna and Ryohei, to take part in Mammon's Test of Adaptability. Under the belief that Kyoko was being held hostage, the trio were forced to solve a series of riddles as well as fight a number of Box Weapons. Takeshi was able to see through most of the illusions thanks to his experience fighting Genkishi. After discovering that Kyoko was safe, they swiftly defeated Mammon and passed his trial. Later Takeshi and the other Guardians were assembled for Reborn's Trial of Leadership and were easily beaten by him. Shortly after, the Guardians joined forces with the other Arcobaleno, to defeat Verde and his army.
When Squalo arrived at the base, he began training Takeshi and while in the woods, Takeshi decided to follow the path of the sword devotedly while in the future. Takeshi was included in the Choice battle during which he encountered Saru, who quickly revealed himself to be Genkishi, who Takeshi was able to defeat using his new Vongola Box. While lying injured Genkishi was killed by Kikyo. Takeshi then went to attack the Millefiore target Deisy and defeated him at the same time as Kikyo defeated Irie. However because of Deisy's undying power, the Vongola lost.
After being sent back to the past for the Inheritance Succession Trials, Colonnello became Takeshi's tutor. During his test, Takeshi assumed it was a fight and began to attack Asari. During the fight, Takeshi noticed an opening in one of Asari's attacks and used it to strike him but Colonnello steps in to try to prevent Takeshi from attacking.
Asari then declared that Takeshi had failed his test, but agreed to give him a second chance, though he refused to give a reason for his decision. Back at the shrine the next day, Takeshi fought Asari again and used the same opening as before. However, he decided in the end not to attack, to which Asari declared that he had passed the test. Asari explained that he set up the attack to see if Takeshi would attack a defenseless man. Later, when the girls were captured by Demon Spade, Takeshi attempted a rescue with the other Guardians. He was separated with the others and fought the doppelganger created by Spade. The illusion was then broken by Hibari's rampage.
Squalo remained at the Vongola Base to fight Zakuro but was caught in an explosion. Later, Takeshi went back to rescue him with Bianchi, Spanner and Giannini. During the final battle against the Real Six Funeral Wreaths, Takeshi arrived in time to defend Ryohei and Gokudera from Ghost. The Vongola eventually defeated Byakuran and after saying goodbye to Squalo, Takeshi and the others returned to the past.
At baseball practice, Takeshi became friendly with Kaoru Mizuno, one of the Simon Middle School transfer students. After the Simon revealed themselves as allies, Takeshi and Kaoru were assigned to protect Tsuna. When he discovered that Kaoru became nervous when people watched him play baseball, Takeshi made everyone watching wear vegetable costumes, so that Kaoru wouldn't feel self-conscious. Kaoru then impressed Takeshi by throwing the ball so fast that it seemed to have disappeared.
A day before the ceremony, in the changing room, Takeshi jokingly suggested that the Simon were trying to get rid of the Vongola after accidently seeing a paper with Vongola crest crossed. Kaoru responded by violently attacking Takeshi and leaving him in a critical state. However, Takeshi was able to write the word "Sin" using his own blood before falling unconscious, alerting the Vongola of the Simon's plans. Ryohei then found him and, after failing to heal him with Kangaryuu, took him to the hospital for operations. The doctor revealed that he would live, but the probability of him walking again was extremely low. In later chapters, after Lambo managed to defeat Ooyama Large, Takeshi is shown in the hospital still wired to machines. Byakuran is then seen standing before him, wings spread from his back.
He later reappears with back to full health to save Kaoru from being killed by Demon Spade. When Kaoru asked why Takeshi saved him after he tried to kill him, Takeshi replies that he would always help Kaoru if he were in real trouble, because that's what friends are for. Demon, quite confused, asked why he was here, knowing that Takeshi should be in a critical condition. Takeshi replied that an "acquaintance" of his helped him recover. Tsuna, looking worried, stated that he doesn't have his Vongola Gear. Upon hearing this, Takeshi revealed under his coat his Rain
Necklace Version X. He called out Ziro and Koziro to merge to Cambio Forma, resulting in the "Two-sword style Vongola Gear". At the beginning of the battle, Demon launched a surprise attack behind Takeshi. The attack was blocked by Kaoru, who said that he knew Takeshi could dodge it on his own, but wanted to pay his debt. After that, Kaoru was taken by the Vindice as he already lost his pride, and the Fifth "Key" was later revealed, but not before asking Takeshi to keep becoming his friend. Enraged at Demon, Takeshi decided to fight him one on one, saying that Tsuna should take a break. Takeshi managed to pinpoint Demon Spade's location and strike him with his new technique, Udachi: Kirisame, and injured Demon in the process. However, Chrome interfered and refused to move when Takeshi asked her to until Demon ordered her to step down. Before they left, Takeshi handed Chrome the Ore of Mist Version X and said that they will always be waiting for her. Takeshi soon fell to his knees (since he was not fully recovered) and decided to take a rest for a night as he told Tsuna and the others that Byakuran was the one who healed him.
At the day of the Simon Rings' awakening, Takeshi watches the fight between Tsuna and Enma and after that goes with the group to encounter Mukuro after he was supposed to have defeated Demon. When Demon reappears by possessing Mukuro's body. He gets trapped in an illusionary world like the others thanks to Demon but he manages to save Chrome from being trapped. After Tsuna and Enma's final showdown with Demon, he is released and receives the final 'key' like the others. A week later, he is seen playing baseball with Kaoru at Namimori Middle's baseball field.
Chrome's Transfer Edit
Takeshi appears with Tsuna at Chrome's welcoming party because Chrome was kicked out of Kokuyo Land. In the miming competition, he isn't seen performing, but laughs at the people's performances.
Later, Takeshi appears the day before Tsuna's father Iemitsu arrives in Namimori, commenting to Tsuna that he was excited to be fighting for Reborn to allow him to revert to his adult form, though he couldn't imagine what it was like.
1st Day of Representative Battle of the Rainbow Edit
Later, on the first day of the Representative Battle of the Rainbow, Takeshi happily heads to school with Tsuna. However, when the battle suddenly starts, he, Gokudera, and Ryohei group up and try to find Tsuna. When an explosion occurs because of Tsuna being punched through the ceiling by Iemitsu (though they don't know the cause), they run towards the explosion; however, they are barred by Hibari and Fon, the former appearing to be Fon's representative, who states that he would bite all three of them to death. Ryohei charges towards Hibari but his battle watch is quickly broken. Takeshi and Gokudera attack Hibari together and use a smoke bomb to get past him. They soon re-group at Namimori Diner where they find out Dino made a deal with Iemitsu stating they would become allies and in return he wouldn't destroy Tsuna's Boss watch.
2nd Day of Representative Battle of the Rainbow Edit
After discussing the situation during the first day battle with Team Uni, their watches announced the start of the second battle and they were ambushed by Team Verde. During this time, Team Collonnelo broke the alliance with Team Reborn due to Tsuna's refusal to leave Team Uni. As the result, Byakuran's boss watch was destroyed while protecting Tsuna, and Tsuna immediately went to where Iemitsu is. With Byakuran defeated and Tsuna left the scene, Mukuro and Fran decides to retreat. Takeshi and Gokudera tried to stop him, but Mukuro was able to escape. Takeshi then suggested for them to go to Tsuna and Iemitsu by riding a nearby bicycle that was boosted by Gokudera's dynamites to increase the speed. Unfortunately, the time limit already over by the time they arrived.
Vindice Ambush Edit
While the Arcobaleno are having a meeting regarding Team Bermuda's participance, they were ambushed by a Vindice outside the battle time and struggle against him. They able to hold up until Reborn arrives, making the Vindice retreat. When they were about to sleep after exhausted from the battle, their watches announces the start of the third battle, not giving them any time to rest.
3rd Day of Representative Battle of the Rainbow Edit
He, Tsuna, Gokudera, and Reborn went to nearby park and encounter Mukuro who later followed by his subordinates. With the three Vindice's arrival, they reluctantly form a temporary alliance with Team Verde in order to defeat the Vindice, knowing they cannot be defeated alone. With their teamwork, they able to rip off the Vindice's robes and witness their true forms along with stone pacifier hanging around their neck. When they restarted the battle, Takeshi was easily defeated by Jaque, as well as Gokudera, Ken, and Chikusa, leaving only Mukuro and Tsuna to fight. After the third day battle is over, he and Gokudera were taken to hospital.
4th Day of Representative Battle of the Rainbow Edit
Takeshi, Gokudera, Chrome, and Fran are fighting against Small Gia and Big Pino who were originally after Team Verde that revealed to be decoy puppets. Small Gia and Big Pino able to find out their hiding place and destroy the illusions along with Takeshi's Shigure Kintoki and Gokudera's Sistema C.A.I. They were about to be killed until Enma saved them with his technique. Tsuna, Enma, and Basil arrives and fought Small Gia and Big Pino. Basil's battler watch was destroyed, enraging Tsuna who attacks, but then his vision was blinded by Small Gia's flash, causing him to hit the flash and momentarily blinded his vision. Before Small Gia could proceed, Takeshi restrains him from behind while Gokudera distracts Big Pino as each of them is holding dynamites. With Enma, Chrome, and Fran's help, they are able to destroy the two Vindice's battler watches without harming both Takeshi and Gokudera.
He is last seen standing outside of Tsuna's house, waiting for Tsuna with the others after being invited by Reborn to celebrate Tsuna's tutelage.