In the past, knowing of his imminent death he decided to transfer his title of successor to a child who happened to be nearby. However the transfer was only partial, for this reason Krishna didn't disappear but was instead linked to Momiji.
After Krishna was beheaded by fake Yama and given Bairi's seal, he seems to be stuck the form of a young child.
While generally calm and collected, when provoked Krishna is merciless against his enemies and will not hesitate to hurt, or even kill them. He is also rather indifferent to the plights of any student besides Rokudou or Yama, who he is later revealed to have been working for.
He seems to be especially devoted to Yama, as shown by how he attempted to kill Sanjuurou when Fake Yama was injured by him.
However, it is stated by the Fake Yama that as a child, Krishna was very fascinated by dead people and the dead spirits that would cross the island.
Krishna considers Rokudou as someone very important to him and will do anything to ensure Rokudou's survival. He goes as far as killing Tomonaga, another student, to take his heart to replace the one Tomonaga has stolen from Rokudou. He also addresses Rokudou with as "Momiji-kun" and is the only person in the series outside of Rokudou's immediate family to address him by his first name.
He also views Rokudou as his leader as he calls Rokudou 'Boss' or 'Commander' on several occassions, though not directly to his face.
Like with Rokudou, Krishna views Yama as someone very important to him. It is later revealed that this is a result of him being a subordinate of Yama. He quickly attacks Hinata when he sees that the other has attacked Yama and is quick to come to Yama's aide. However, he is only loyal to the real Yama, who apparently is not present in the school and has been replaced with a fake.
He fights with a gigantic sword.
He also appears to have an immortal body as he has been able to survive attacks that would have killed normal people. For example, after Tomonaga stole Rokudou's heart, Rokudou was still able to transform into Krishna and Krishna was able to move freely even without a heart. He also did not seem to notice that he lacked a heart, until it was pointed out by Aira. He can re-attach any lost limb or body part, which is seen during his fights against Tomonoga and Hakua.