Seriously what was up with ep.18 ?
Yukki's dad kills his(Yukki's) mother. He doesn't explain why, he doesn't deny it, and he tells Yukki he can't prove it. So Yukki tries to expose him and discovers that "he feels sorry he killed his mother". And he forgives him.

The first half of the episode was ok though. Little Yuno-Insanity mixed with comedy relief
PS
PSS: Does anyone else like "Murmur-sensei's side-story diary"?