What!? I'm the Tenth Generation Mafia Boss!? (えぇ!? 俺がマフィアの10代目!?) is the 1st episode of the Katekyō Hitman Reborn! anime.
The first scene of the show takes us to Sicily, Italy. Reborn walks down a street, with everyone staring after him in fear. After he enters a bar, he states that he is heading to Japan. A man previously seen attempts to kill him, to which Reborn points at him a transformed Leon. He then refers to himself as the "Home Tutor Hitman, Reborn!"
The scene then shifts to Japan in the early morning. Reborn is then seen getting off a bus and putting a message inside the Sawada mailbox. We see Takeshi Yamamoto run by for morning practice, and Nana Sawada goes out to get the mail. She reads Reborn's message.
The day then progresses until it is late morning. Nana tries to call her son, Tsunayoshi Sawada, down for breakfast, stating that he is going to be late. When that fails, she goes upstairs to try to wake him up herself. She happens to see another math test he has failed and, using that to wake him up, tells him that he will have a home tutor starting that day. After Tsuna falls down the stairs, Reborn is seen inside his house, telling Tsuna that he will be his home tutor. Tsuna laughs at this but abruptly stops when Reborn beats him up.
After running outside to go to school, Tsuna is scared by a chihuahua whose leash became loose. Reborn tells him that he is a pathetic loser, and we meet Haru Miura peeking at them from behind a wall. She tries to go out and hug Reborn, but is interrupted by Kyoko Sasagawa, who gets there first. Tsuna reveals his crush on Kyoko, stating that she is the "idol of Namimori Middle School." Reborn automatically notices Tsuna's crush on Kyoko, and tells him that the only reason he hasn't confessed yet was because he was "No-Good Tsuna" (Dame Tsuna). After that, Reborn shoots Tsuna for the first time with the Dying Will Bullet so that he could confess to Kyoko. Tsuna runs towards Kyoko in his underwear, screaming that he will "confess with his Dying Will."
While running, we see Ryohei Sasagawa, who exclaims that his punches are "extreme" today. He sees Tsuna running straight into a truck, and wonders what was wrong with him. Tsuna bounces off a fence and lands right in front of Kyoko and Mochida. After he confesses, Kyoko runs away screaming, and Mochida punches him. Tsuna gets out of Dying Will Mode extremely embarrassed, after which Reborn floats down in a parachute and explains the Dying Will Bullet. After that, Kyoya Hibari arrives and tells Tsuna that classes have begun. Inside his classroom, Tsuna is mocked by his classmates, and a person tells Tsuna that Mochida was challenging him to a game of kendo.
Inside the gym, everyone thinks that Tsuna has run away. However, when Tsuna does eventually arrive, everyone laughs at him because they knew that there was no way Tsuna could win. Mochida tells Tsuna that he only needs ippon, or one point, to win. Tsuna tries to run away, but is then shot with a Dying Will Bullet from Reborn. He jumps upon Dying Will Mode, and tackles Mochida, ripping his hair out and states that he had "hyaku-pon," or one hundred points. The judge, who Mochida rigged to be on his side, is hesitant to raise his flag. Tsuna, noticing this, continues to rip hair out until the judge declares him the winner. The crowd cheers, and Kyoko tells Tsuna that the only reason why she ran away was because she didn't know what to say. Outside the gym, a silhouette mutters to himself.
At home, Tsuna is shocked to hear that he was the Vongola Famiglia's Tenth Boss. Reborn states that the only reason he had arrived from Italy was to train Tsuna to become just that. He summarizes by saying that because Tsuna had the Vongola blood, he must become Boss. He falls asleep, and Nana later comes in and wishes Reborn luck on training Tsuna.