As Tsuna sits in class, Lambo arrives and informs Tsuna that he can't pee since his zipper is broken, causing the class to laugh. Tsuna tries to take Lambo to the bathroom, but Lambo stops when he sees Reborn and pees his pants, embarrassing Tsuna. At home, Tsuna confronts his mother about Lambo, but Reborn suggests that he find Lambo a babysitter, saying that he can refer Tsuna to some of his acquaintances.
The next day, Tsuna is surprised to see that Hayato and Takeshi are the ones that Reborn referred. Lambo then arrives and Hayato immediately argues with him and kicks him. When Reborn announces the start of the babysitter compatibility test, Hayato refuses while Takeshi accepts. But when Reborn tells them that the winner will also be Tsuna's right hand, Hayato agrees and lies, saying that he likes Lambo. After Reborn explains the rules, Hayato volunteers to go first. When he approaches and reaches for Lambo, Lambo puts a grenade in his hand causing Hayato to strangle him in fury. When it's Takeshi's turn, he gives Lambo a baseball glove, planning to play catch. However, his plan backfires when he forgets to restrain himself and throws the ball at full force to Lambo's head, causing him to cry even more.
Suddenly, Haru arrives and picks up Lambo trying to stop him from crying. However, Lambo uses his Ten Year Bazooka on himself, causing Haru let go of him since she'd never seen Lambo's future-self before. As future Lambo tries to introduce himself, Haru slaps him, saying to button up his shirt or she'll report him to the police and thinks him a pervert. After Hayato bullies Lambo, Lambo tries to go but leaves his horn behind. Takeshi throws it at him with full force causing Lambo to cry again. Reborn then announces that Tsuna will be the one to babysit Lambo...
*Note: Bold + Italicized = First Appearance