Tsuyoshi Yamamoto is Yamamoto's father and one of the wielders of the Shigure Soen Ryu sword style. He runs a sushi bar named TakeSushi with the help of his son and even trained Yamamoto to use the Shigure Soen Ryu. Tsuyoshi Yamamoto is very proud of the Shigure Soen Ryu style and even gets angry if anyone suggests that it isn't capable enough or weak. He is generally very perceptive, often able to tell his son's feelings just by looking. He has a kind nature, a trait inherited by his son. Takeshi Yamamoto is extremely proud of his father, as he often refers to his fighting style as "his old man's Shigure Soen," and often proclaims that it is the strongest and second to none.
He is usually clad in a white shirt and a white band wrapped around his head. Him and his son look a lot a like with the way that the both have black hair color and brown eyes.
Tsuyoshi first appeared when Tsuna ate at TakeSushi with Reborn, Bianchi and Lambo, who did a "dine and dash", meaning that they ate without paying for the meal, forcing Tsuna to work at TakeSushi for a while to pay off their debt.
When Tsuna was hospitalized because of his injuries from Death Mountain, Yamamoto came to his hospital room for support. He decides to bring Tsuyoshi, his dad. Tsuyoshi brought a big green bag with his sushi-making table inside and his small blue bag with supplies and food like his knife and fish. Tsuyoshi made authentic Japanese sushi for Tsuna. Tsuyoshi left the room to go back to his shop and told his son to take care of the rest.
When everyone arrived in the future, they were informed by Reborn that Tsuyoshi was killed by the Millefiore Famiglia. However, after Tsuna defeated Byakuran, they were told that the future changed and all disasters caused by Byakuran and the Millefiore would be undone; thus, Tsuyoshi would still be alive.
- Takeshi Yamamoto and Squalo had 7 common forms and only one different, which means Tsuyoshi and the person who lost to Squalo had the same master. He taught them all 7 forms and then both of them eventually created two different 8th forms.
- In Mr. Rebokku no Ciao Ciao Interview, Yamamoto stated that his father Tsuyoshi was the one person that he thought he couldn't beat.
- From Haru Haru's Interview: Dangerous, Takeshi Yamamoto states that back when he was little, Tsuyoshi was very stubborn, not allowing himself or his son to eat anything with a foreign name in it. This led to Tsuyoshi creating his own unique names for certain foods. A color would be added at the beginning of the name depending on the color of the noodles; however, if the food could not be color-coded, it was not allowed in the Yamamoto household. Some examples include:
- Salisbury Steak = Small Round Meat Patty
- Curry Rice = Tenjiku Rice with Broth
- Spaghetti = Western-Style Fried Noodles or Yakisoba (in Japanese)
- Neapolitan = Red-Western style Fried Noodles
- Carbonara = White-Western style Fried Noodles
- Squid Ink = Black-Western style Fried Noodles