One night, a burglar makes their way into Tsuna's room, causing Tsuna to faint due to his fear of burglars. Upon waking up, he assumed it was simply a dream until discovering a man's body lying in his room. Reborn then appears and informs Tsuna he had used Hyper Intuition to kill the burglar the night before due to automatically going into Dying Will Mode from being shot by the Dying Will Bullet countless times. Gokudera arrives to relay similar information to Tsuna.
In the manga, Reborn said that Tsuna shot the burglar automatically using his "self-defense mechanism". Tsuna also did not wake up in the middle of the night to see the burglar and it was in the morning when he first sees him. Also, Tsuna had seemed to have shot and killed the burglar after waking up. Reborn had also placed a gun in Tsuna's hands, showing the 'evidence' that Tsuna's killing instincts has awaken.