Tsuzuki Asato
Tsuzuki in the manga goes through partners like he does with Apple pie (his favorite dish).  Then Hisoka showed up and they just seemed to get along, to a point.  Many things happend to them and they lean on each other for support like good friends.

Tsuzuki didn't have a very pleasing life.  I don't know for sure but I have heard that he just couldn't handle all the things that would go on around him so he would try to kill himself failing each time and he would go in and out of insane instatutions where Muraki's grandfather would work and experiment on his beautiful patient.
Name: Tsuzuki Asato

Birth date: 2/24/1900

Blood type: B

Height: NA

Age: 26 (eternally)