saiko

Menhera kei = yumeleep. Look at all the cute in their videos, you'd never think they were singing about dying and being fucked in the head. Also the singer loves giving the middle finger. 

Here is more about the fashion style and culture of menhera kei that @Komorebi mentioned earlier: https://fymenhera.tumblr.com/info

I think the band gozenreiji. fits the theme? The singer tends to talk about wrist cutting.

AvelCain, R-shitei, Amai Bouroku, Savage, Depain, Meary, Zigzag, Gossip (both old and new, to an extent), 0.1g Gosan, Mathilda (kinda), Yumeleep, SHELLMY (probably), and probably 3-dozen other bands would fall somewhere onto that spectrum. It seems to be less of a subgenre, rather than an aesthetic, although bands that fall under it tend to sound like R-shitei or Savage.

I know it's been used within the scene itself, so I don't think it's solely a web-generated term (Meary had an album named "Menheler-ism", and there was a history of vkei video the lead singer of Golden Bomber was in where they discussed how today's vkei uses "mental illness as a subject" or something to that extent). Mental illness and self-harm are definitely not new subjects in vkei, or music in general. The concept has just been more stylized and #branded than it has been in the past. Had time been rearranged, groups like Mucc or Earl Grey probably would have been considered part of that scene just based on lyrical content.