I do a lot of visual kei vocal covers, I would say that the techniques aren’t particularly unique compared to other genres, just the way they are employed.
Many of them sing more towards the mask when it comes to positioning, ie the front of their face, so it might be worth looking into vocal placement techniques.
With this you can make the sound more bright without making it sound overly nazally.
A lot of them have quite “home made” techniques though, and are somewhat sloppy with things like support and breath control, but I don’t think this is the case with the 3 bands you listed (I’m not too familiar with them)
About the “fake” vibrato; I don’t know about the bands you mentioned but with some other singers the reason people say it’s often “fake” is because vibrato is something that happens naturally in your voice when the support muscles and compression are properly dialed in, but in many cases in VK they emulate this sound by modulating the pitch, so essentially a trill. It’s not a bad thing though,
and it does have a different sound to it, which sounds somewhat distinctly VK compared to pop singers who usually vibrato the more natural way, but there are a lot of VK singers who do it the natural way too.
I’ve noticed a lot more VK singers using fry for different kinds of screams and sounds these days too. You can do a lot with fry and it can be utilized in basically every register to some degree.
You can make thin vocals sound really powerful with it to, many power metal vocalists use it that way, and Chester Bedington did for example
As for the highs that some vocalists like Kyo, Lime and Mama’s vocalist do, around their A4-F4 range is a mix voice and higher than that is a well supported head. Lime’s mix is crazy good though so it’s hard to tell where it begins and ends.
Kyo does a heady mix while lime does a chesty mix. For that kind of thing it might be worth watching some of Chris Liepe’s videos. Those kind of highs are pretty hard to get dialed in at first, it took me a long time to be able to sing a lot of Dir en grey’s stuff.
And of course kyo uses whistle register too, usually with fry, to get really high and wailey. Again it uses a lot less effort and power than it sounds, but the fry just makes it sound so huge and piercing.
Did I mention how useful fry is?
Oh and VK singers use a tonne of falsetto, especially the ones who never use mix voice in their music
Overall I think the most important things to learn about as a beginnner are proper support and how to project your voice, as well as placement of your vocals. Support will help you with stamina, accuracy, volume control and projection… Support really is the key to improving every other area of your voice, and I learned this the time consuming way.
You can feel the support sensation in your abdomen if you blow really hard through a straw for example, or try to blow out a candle quite far from your mouth.
Sorry I’m really bad at explaining stuff well, I’m mostly self taught and picked up on terminology and stuff quite late.