He was born into the Estraneo Famiglia along with Chikusa and Mukuro. All three of them were being experimented on as "guinea pigs". However, he and Chikusa were later saved by Mukuro, who had annihilated the entire Estraneo Famiglia. Ever since that massacre, they have been Mukuro's loyal subordinates.
List Countdown Edit
Ken is the first of Mukuro's gang seen targeting an unnamed character. Later, he tracks down Ryohei, who asks him to join his Boxing club. Ken accepts the proposition on the one condition that Ryohei beats him in a fight. It is implied that Ken defeated Ryohei because he is later seen in a hospital. It is at that time that Ken pulled 5 of Ryohei's teeth. (In the anime, he gave him a watch that read 5 o'clock.), showing him to be the fifth strongest Nami-Middle student.
Kokuyo Land Invasion Edit
At Kokuyo Land, Ken throws dead dogs at Tsuna's group, presumably to move them closer to the Botanical Dome. When Takeshi falls through the roof, he jumps in after him. He is amazed at how ditzy Yamamoto is in thinking that the dogs were actually puppets. Ken begins their battle by charging Takeshi, and when his opponent evades, he uses his momentum to leap into the air, put in the Monkey Channel, and then do a spinning wall-jump back towards Takeshi, who brings his bat out to defend. Ken uses the jaws of his Channel to destroy the bat with little fanfare. His opponent is visibly angered, but first asks him how he managed to change his appearance. Ken equates putting a new disc into a video game console to him putting teeth into his mouth to change his Channel. He demonstrates by switching the Monkey Channel for the Kong Channel, and heaving Takeshi into the glass walls of their arena. Off-screen, he switches to the Wolf Channel and reveals that because of the dead dogs' blood of Takeshi, he can smell him, while he can't be seen. And Ken proceeds to launch a flurry of quick attacks, which Takeshi dodges, trying to protect his arm. Reborn kicks Tsuna down into the arena, and Ken changes targets to the much weaker person. However, Takeshi throws a rock to get him to refocus on him. Ken charges and sinks the teeth of the Cheetah Channel deep into Takeshi's arm. However, he fell for the trap, and with a swift sword-butt to the temple, was knocked out by Takeshi.
He taunts Tsuna's group after Takeshi and Tsuna are helped out of the hole, revealing that he managed to instantaneously switch to the Opossum Channel to effectively play dead. Bianchi proceeds to drop a large rock on his head (manga only).
Ken reappears when Hayato is winning against Chikusa. He takes advantage of the fact that Hayato was suffering from Shamal's Trident Mosquitoes' countereffect, and digs the claws of an unknown Channel deep into Hayato's chest, which was the debilitating blow that won them their fight. As he watches his and Chikusa's opponent stumble and fall down a flight of stairs, they dawdle and give him time to release Hibari. He is defeated off-screen and tossed out of the window.
Mukuro Face-off Edit
Ken and Chikusa appear when Tsuna was told to buy drinks after he questioned who the Mist Guardian is. When he reached the shop, however, Tsuna immediately fainted when Ken surprised him from behind. After a short conversation with Reborn, he and Chikusa left as he saying that Tsuna's Mist Guardian is too good for him. He later appear again in the gym where Mist Ring Battle took place, escorting Chrome. After Mukuro defeated Mammon, he changed back to Chrome who was exhausted and fell asleep. Ken and Chikusa left without her, stating that she isn't Mukuro and has no intention to give her his concern when Tsuna questioned them.
He and Chikusa watched Hibari's fight under Mukuro's order. During Gola Moska's rampage, they saved Chrome from the mines that buried within the ground that she accidently stepped on. This left them unguarded and trapped between Gola Moska and rifle pointed at them. Fortunately, Tsuna arrived in time, protecting the three of them from both attacks.
He and Chikusa secretly followed Chrome to the last match, but was found out by the Cervello and was told to stay and watch outside the battlefield along with Reborn, Colonnello, Basil, and Shamal until the match ends.
Battle with Glo Xinia Edit
Ken, along with Chikusa, makes a cameo appearance during Chrome's battle with Glo Xinia in a flashback. He was talking about their secret hiding hole and put gum in it, after which Chikusa commented that gum was not food. Ken, along with Mukuro and Chikusa, makes another appearance during Chrome's battle with Glo Xinia. All three of them appear as Real Illusions made from Chrome, with the help of her Vongola Mist Ring.
He appears with Chikusa when Kyoko, Haru, I-Pin, and Bianchi came to Kokuyo Land, asking where Chrome is. He replied, saying that she'd been missing since the day before yesterday (when Tsuna and the others came back from the Future). He also said that she ran off without saying anything, and that he will give her the rice balls when she comes back. While he was eating some snacks, Chrome comes back in tears, confusing both Ken and Chikusa. He tried to cheer her up by offering some snacks, to no avail. He and Chikusa commented that Chrome wasn't acting like herself. The next day, he and Chikusa met Tsuna and the others on their way to Kokuyo Land. He immediately blames Tsuna and the others about Chrome's condition.
After he and Chikusa explains the situation to Tsuna's group, he decides to go and buy some snacks, stating that he's hungry. But, Chikusa immediately realized that he was going to buy some chocolate for Chrome, which Ken hotly denied, saying that he was going to buy them for himself. He returns after buying many snacks in hopes of making Chrome happy, but is shocked to find out the whole Kokuyo land building has disappeared. When Kokuyo Land appears again after Demon Spade's defeat, he immediately yells at Tsuna to give an explanation, but changes his mind when Chrome apologizes and realized that she came back to normal which makes him happy but hides it immediately by saying that if she cried again she will have it for good, to which Chrome happily replied yes.
Ken appeared alongside Chikusa and M.M. after Fran freed Mukuro from the Vindice Prison. When they all arrived in Japan, they engaged Zakuro in combat, where Ghost came out suddenly and absorbed Zakuro's Flames. Ken also watched the fight between Tsuna and Byakuran. After Tsuna defeated Byakuran, Ken was seen with Chikusa and Mukuro calling out to Chrome that it was almost time they went back to the past.
Tsuna called Chrome at Kokuyo Land for a meeting with the Simon Famiglia, but Ken hung up on them. Later, he was happy when he, Chrome, and Chikusa received a package with food from an unknown sender, who was actually revealed to be Julie Kato.
Searching for Fran, Ken, along with Mukuro, Chikusa, and M.M went to countryside in France called Jura in order to recruit Fran into their team. However, when Mukuro's furious that his hair being compared to pineapple and Belphegor started to attack Fran with his knifes, Fran running away. Ken tried to stop and convince Fran that they're his allies but Fran immediately mocked Ken's habit on saying "byon" with smiley face, assuming him as an idiot fairy and tell him not to touch him or else he would catch his stupidity.
1st Day of Representative Battle Edit
Later, after Mukuro was requested by Verde to fight for him, he is seen in Namimori accompanying Mukuro on his "declaration of war" statement to Tsuna. He and M.M protests when Verde starts to mock Mukuro, calling him a runt.
2nd Day of Representative Battle Edit
During the second day of the Representative Battle of the Rainbow, he, along with Mukuro, Chikusa, and Fran, fought against Team Reborn and Team Uni. However, when Colonnello fired his Maximum Rifle attack, his and Chikusa's wristwatches were destroyed, thus disqualifying them from the battle.
3rd Day of Representative Battle Edit
During the third day of the Representative Battle of the Rainbow, Ken and Chikusa uses the remaining two spare wristwatches, allowing them to rejoin the battle and help Mukuro to fight the Vindice with Team Reborn who had formed a temporary alliance with their team. However, he, Chikusa, Yamamoto, and Gokudera were easily knocked out by the Vindice after their true form was revealed. After the third battle was over, he and Chikusa was taken back to Kokuyo Land along with Mukuro to treat their injuries.
4th Day of Representative Battle Edit
He and the other Kokuyo Gang members along with people who Tsuna had talked to gathered at Tsuna's house to discuss plan to defeat Team Bermuda. After the battle was over, he, Chikusa, and M.M visits Mukuro, Chrome, and Fran, in hospital and he is seen lying on Mukuro's bed with Chikusa and Chrome beside him when Hibari destroys the wall of Mukuro's room.