saiko

MenheraKei is basically any kind of Vkei with mental health themes (generally pills and wrist cutting). Examples include R-Shitei, AvelCain, and GossiP. It's not really a genre, just a fan-made term I think. Please correct me if I'm wrong lol

Thanks. I supposed it involved some kind of specific aesthetic in terms of sound -but it's seems to be just a theme over lyrics rather than anything else. 

Thanks!

Yeah, its' a blog/net term adopted by bands to talk about teen issues. Nothing to do with music per-se, really.
There's also a fashion movement associated to it (unrelated to VK).