Tokage

The only japanese autism musician who I know is the composer Hikari Ōe, and yes mental "ailments" is still  a taboo in Japan , only few musicians talk about this subject like Ryo the singer of Baroque and Kannivalism who suffered of adjustment disorder.
He had written  his autobiography Utsu-byo Rocker (Depressed Rocker),  in his book Ryo describes his grueling struggle with the illness in five chapters each called 'Mental Breakdown', 'Adjustment Disorder', 'Life in Hospital', 'Return to Society' and 'Life and Death'.

You also have Fukase the singer of the jrock band Sekai no Owari he was interned in specialized institute for treat his attention deficit hyperactivity disorder

I guess we may also add ex-D.I.D. to that particular category, as IIRC he's been diagnosed with BPD if I'm not mistaken. 

it's still kind of sad that such things are so stigmatised over there, but at the same time, I guess they still are to some extent in the rest of the world as well, so...

The major problem is for many asian countries (Japan, China, Korea, Philippinnes,Vietnam, Hong-Kong,Singapore etc...) they associated that with weakness, guilt, and shame.

For them say to their familly or friends they suffer of mental "ailments" they will "lose their face" infront of them and in asian societies when you 'lose your face" you lose your social standing, reputation, influence, dignity, and honor, so for "save their face" they prefer keep that for them.

I hope one day they will change their point of view about that.