Kokuyo Arc

We begin the Kokuyo Arc with the discovery that someone is going around beating up Namimori students and removing their teeth. We first see these strangers beating up one of the prefects - what appears to be one of Hibari's underlings (since he has an exagerrated pompadour hairstyle). Tsuna and Reborn are walking to school discussing the recent attacks when Hibari appears to tell them that it isn't a gang-related attack. He proceeds to tell them that he has to stop whomever is harming his students when the Namimori theme song begins to play... and we find out that it is Hibari's ringtone. He tells Tsuna that Sasagawa Ryohei was just attacked.

While visiting Ryohei, we overhear from Kusakabe that Hibari has disappeared after the attacker's trail. We then see Hibari taking down countless baddies until he reaches the mastermind who tells him that there is a new order in town. Hibari, naturally, will not have it. He threatens to bite the mastermind to death.

However, when we switch back to Hibari, we find that the mastermind has discovered his weakness to cherry blossoms. The mastermind, soon revealed to be called Mukuro by his subordinates, is seen holding a bloody but defiant Hibari by his hair. Later, when his subordinate asks about "Duck," Mukuro reveals that he took him out and they'll just leave him unconscious.

Later, after Tsuna and his group decide to go to the Kokuyo base to find the culprit. Tsuna meets a Kokuyo student who we know to be Mukuro, but Tsuna does not. Mukuro pretends to be a hostage in order to get information out of Tsuna about who has come with him. Tsuna asks him if he knows where Hibari is, to which Mukuro responds that he is being kept by the bad guys. Mukuro becomes suspiciously curious about Reborn, and Tsuna gets freaked out and makes an excuse to leave.

During Gokudera's fight with Chikusa and Ken, his old wound is reopened and he is lying at the bottom of the stairs. He sees the bird of one of the already defeated Kokuyo enemies, but the bird is singing the Namimori theme song. Gokudera starts laughing and blows up the wall behind him because he knew the only person who'd like the terrible anthem was Hibari. Sure enough, Hibari is sitting among the rubble.

Despite his terrible injuries, Hibari beats the two up like a boss. He proceeds to stop Tsuna from being killed by Mukuro's illusory snakes while carrying Gokudera into the room... but then he just throws Gokudera on the ground, saying the debt is repaid between the two of them. Hibari fights with Mukuro once again. Reborn tells Mukuro not to underestimate the heavily injured Hibari, to which Mukuro questions the outcome of their duel had Hibari been at full strength. He then summons more cherry blossoms to incapacitate Hibari, who then gets in several good hits. Gokudera had given him the antidote for his Sakura-kura disease thanks to Dr. Shamal's thinking ahead. Mukuro falls, and so does Hibari. Reborn informs Tsuna that he has been fighting unconsciously since halfway through.

However, Mukuro is not done for the count. To everyone's surprise, he puts a gun to his head and shoots himself. However, this is soon revealed to be a method to possess the bodies of Tsuna's fallen friends. He at one point attempts to possess Hibari's body, but falls over as he punches Tsuna. He mentions that Hibari's body can't be used, and that it was frightening that Hibari was fighting him in that physical state.

After Tsuna defeats Mukuro, the Vongola medical team arrives and carries everyone off on stretchers, Hibari included. He is then seen sleeping, his new best friend the bird by his side, on the Nami roof, yawning when Kusakabe tells him the baseball game has started.