I read the translations for this way back when even the concept of scanlations wasn't around yet. Yeah. Old school text translations. I'm not sure if it's since been picked up, but I still want to look for it.

I think the title had something to do with blue stone? The manga is probably early to mid 90s, and was a series. It was about angels, the main characters being Mikael and Fillanzia, and the power of a mysterious and powerful blue stone that I think Mikael has in his possession? I think Fillanzia was the happy-go-lucky one who was really attached to Mikael....

Sort of like Shuw Morimoto's Asterisk, I guess.

I would love if anyone is able to help me out! It's been bugging me for a while! (And Google won't turn up with anything. 🙁 )

And I think it had the word Sonata in it?

Totally guessing here, but could it be this: Matendou Sonata

The "blue stone" thing suggests it might be Lapis Land Sonata.