Over the past few days, I've been making my way through the Death Note musical. I had no idea that this existed and its really weird. I kinda like it though.
I haven't heard of any other musical adaptations of anime, but I suspect there isn't many. After thinking about it, I've come to the conclusion that Death Note might be the absolute best candidate for a musical adaptation, at least out of anime that I'm aware of. Its short, characters are built around conflicting ideologies, the main character's tragic fate is established at the beginning, and it features gods lamenting over humanity. It was litterally ripe for this kind of thing.
Overall I really enjoyed the first half, but things start to fall apart later in the show. I think the ending just feels a bit too rushed. The music is pretty good though. I might look for more anime musicals, assuming that they're a common thing.