Hi Mycernius. Thanks for your interest. I hope you'll find at least something to go on. It can always be hard zeroing in on potential favorite bands. I've only recently gotten a good taste of what kind of amazing bands are there after years of trudging through popularly discussed yet mediocre artists.
I've heard good things about ryuichi sakamoto, though i've unfortunately never had the chance to listen to him. He does synth-based music, correct? Anyway, I'm absolutely in love with his daughter, but that's my little secret
Let's get down to the gritty. I can't write much on them due to time, but I hope you'll at least check out my recommended ones. My choices will probably be relatively on the mellow side, but if you want something harder, let me know, since I still have a bunch up my sleeve.
POPULAR ARTISTS (usually appeal to younger folks, but still may appeal to adults)
Yoshiki, from the metal band X Japan, has done some classical works. It's more pop-classical than classical-classical, but the songs are nice enough to listen to. The CD ETERNAL MELODY I has orchestral arrangements of some X Japan songs.
B'z - I don't listen to them that much, but they're fairly popular, using very blues-y guitars and having an Aerosmith-like aura about their music. Pop.
Spitz - they're a fairly mellow, mature band that does adult alternative (?) rock. The vocalist has a very husky voice, and may take some getting used to, but it's good and not nasally, I don't think. Recommended.
Sugizo - ex-Luna Sea. He's done a number of collaborations with other artists, and is one of those pretty-prominent-but-not-much-discussed geniuses, considering he's done a fair number of collaborations. To describe him might be a wasted effort, but he gravitates towards lush soundscapes and compositions, utilizing, but never overdoing, electronics (TRUTH and REPLICANT TRUTH albums), beautiful acoustics and violins (Rest in Peace and Fly Away song, and other tracks on the SOUNDTRACK soundtrack), and beautiful electric guitar effects. He's one of those wonderful artists who will never get stagnant, and I don't think any of his songs can be classified in any genre, least of all pop or rock. Highly recommended.
Nobuyuki Hirakura ツ− Obviously L'arc en Ciel is a group that deserves mention, considering its wide range of styles, but if you like acoustic guitar arrangements, this is definitely a good listen. Unfortunately, his arrangements are out of print, so you have to look around some communities to find it. Or you could just ask me. Recommended.
Gackt ツ− I love Gackt, but adults seem to steer clear, considering his eccentricities. Recommended if you want to take a risk.
Hyde ツ− While his second album 666, probably needed more work, I highly recommend his ROENTGEN album. Lush instruments and orchestration underlying a soft yet strong voice.
Yoko Kanno ツ− known for various anime compositions. A genius. Worked a lot with Maaya Sakamoto, in which the works tended more to the pop side, but her solo albums, 23-ji no ongaku and song to fly, include a lot of beautiful instrumental pieces. Highly recommended.
Thee Michelle Gun Elephant ツ− Is this the right name? Don't know, but if I recall correctly, their music is very classic-rocky, lacking the clean refined-ness of other j-bands, with maybe some hints of blues? I obviously don't listen to them much.
LESSER KNOWN ARTISTS (harder to find)
The indigo ツ− I've only listened to RECORDS. Mellow adult alternative (?) pop. Uses acoustic (st strng) guitars a lot.
Paris Match ツ− Smooth jazz band. Refined, lush compositions, beautiful basslines, and a female vocalist whose vocals are perfect (well, if there's anyone who's a perfect singer, it's Risa Ohki, but I digress). Highly recommended.
Yae ツ− cultural-inspired music with a very pastoral aura to it. Soft and tranquil and an absolute bore to some people used to faster stuff. She's another recent favorite. Highly recommended.
You can also try checking out
http://nippop.com/browse_artists/ At the very least they have Paris Match, which is always a good thing. Also, feel free to PM me, as well. It's my pleasure to help out!