An insane 日本动漫 character?

Ladd Russo From Baccano

Mephisto doesn't exactly seem like the most mentally healthy.
An oddity among demons and insane among humans.
Oh, how I 爱情 Mepphy~ <3

Shou Tucker from FMA, who first turned his wife into a pained monster just for a research grant, and later later did the same to his dog and child.
Don't 你 find this sick? XC

Karma Akabane from Assassination Classroom is one insane and sadistic kid.

Yuri Petrov from Tiger and Bunny. Anyone who stands on a rooftop in the middle of the night in a 斯潘德克斯弹性纤维, 氨纶 suit and rants about the voice of Thanatos needs help.

Donquixote Doflamingo (One Piece)

Harime Nui from Kill la Kill. She gives me chills down my spine just 由 thinking about her.

The majority of the cast of Higurashi no Naku Koro ni.
Below: Ryuuguu Rena.