what are some japanese singers with good voice?
 

i want to hear.

There are many, but here are a few:

-- Utada Hikaru -- "Stay Gold"


-- BoA -- "Do The Motion"
(note: She's actually Korean, but has established herself as a Japanese artist)


-- Maaya Sakamoto -- "Kaze Machi Jet"
(note: The song starts at about 0:33)


-- Sowelu -- "I will"


I posted these songs particularly for the quality of the vocals.
I wasn't sure of your taste, so I tried to make them somewhat diverse, in terms of sound, range, genre, etc.

As for male singers... I don't listen to a lot of slow songs by males (or -- at least, not anything really vocally demanding). I'm sure someone else might be able to tell you some good male vocalists.

Ken Hirai, Namie Amuro, Da Pump lead singer cannot remember name, and Utada Hikaru come to mind.