I've been digging around for a while, and I want to say that at least Murai is his real name. Especially since he only specified in the interview that "Seiya" wasn't his real name, and he's used Murai for such a long time.
Additionally, I looked at the game credits of some old Konami games and several of them credit him as "Kiyoshi Murai", with occasional nicknames such as Kiyoshi‑μ and K-Mu (it wasn't too uncommon for Japanese developers to use nicknames in game credits, take Zelda and Castlevania for example). Specifically, Kiyoshi appears in credits up until May 1994, when Tokimeki Memorial was released. The Genesis version of Animaniacs was released earlier the same month and credits Kiyoshi "K-Mu" Murai, but Tokimeki Memorial credits Seiya. After that he seems to consistently be credited as Seiya Murai. It seems redundant to come up with a nickname if Kiyoshi Murai already is a false name.
Naturally, I'm only speculating about all this and nothing is confirmed to be true. Kiyoshi might be his real name, but he figured that he didn't want to use it anymore due to his shyness. It could also simply be a pseudonym he didn't like anymore, and replaced it with Seiya. It all seems a bit suspicious to me. The only way to know for sure would be to ask him, and I don't think that will lead anywhere.
- This is a really interesting bit. I'll try to look for more information about his real name, thank you! --FinalOffset (talk) 00:01, 10 March 2015 (UTC)
- A little update: Mighty Guy is credited to Kiyoshi Murai in the JASRAC database. --FinalOffset (talk) 14:31, 3 April 2015 (UTC)
- So he changed his Facebook name to Kiyoshi Murai as well, and he talked on his twitter about the Genesis version of Animaniacs. --FinalOffset (talk) 13:46, 30 March 2019 (UTC)