I've been watching a lot of anime recently and realized whether the music fits a scene or not affects a lot in how much I like it, so... who's in charge of doing so?
Is it the Episode Director, the Series Director, the Sound Director or someone else? Or maybe it depends on the series?
You might want to read this article by Justin Sevakis because it really varies and depends on the type of production committee.
TL;DR
Anime opening and ending themes are a big deal not only for fans, but for the creators, and the companies producing anime. Opening themes are a show's "best foot forward," and the staff will usually put quite a bit of effort into coming up with an impressive sequence for whatever song is chosen. Anime production committees, the group of companies putting up money to produce the show, often include a record label or music publisher, and so those theme songs are valuable places to promote their artists. Ads by Kiosked
In some cases, the director will go into the project already wanting a certain existing song, or wanting to work with a particular artist to compose something specifically for their new project -- regardless of whether that artist has anything to do with the companies on the production committee. That's how we very occasionally get English artists doing opening or closing themes. Other times, the production committee will insist on using the songs to push a specific artist, and the director just has to deal.
The business of anime vocal tracks is nearly always facilitated by the main production company or another business on the production committee. Many major anime producers also have affiliated record labels -- for example, Bandai Visual owns the record label Lantis, while Aniplex itself is a division of Sony Music Japan. At an early stage, the production committee has a meeting with the director of the anime, and presents him with a pile of pop songs that are in production. These songs are at "demo" stage -- meaning, they're not done, and usually have a temporary vocal track. The director usually just picks a song from that pile and uses it. They might tweak the lyrics a little bit to fit the show better. The record label will then go back and finish the song with the artist of their choosing, who may or may not be a voice actor featured in the show. If a famous (expensive) composer is doing the music for the show, they will often be asked to contribute the theme songs, as they're likely to be hits no matter who sings them.
The business of anime songs is a huge one, and operates as a market separate from the rest of the Japanese music scene. The selection of song and artist is therefore usually a business decision.
