Episode 1 spoilers about themes

Zettaiken said:
Treachery isn't simply a "Aizen's Theme" just a normal ost which studio uses, which was used many times and even in fillers, the first usage is actually from filler arc 177th episode 6:53 when Ririchiyo is attacked by an enemy [I ain't good with memories of filler stuff]. Outside series it has debuted for 2nd movie Diamond Dust Rebellion [most of osts which haven't appeared in first arcs were actually debuting in movies] and funny enough the Treachery chorus played exactly when Renji activated his bankai at around 1 hour and 14 minutes of the movie when they are climbing that tower to defeat Kusaka. Aswell as it has been the theme for Nnoitra's Ressureccion and quite a bit of other scenes including Aizen's vs Everyone famous scene.

In TYBW it has also appeared in previous cour, when Ishida betrayal happened it is the Ominously remix and Treacherously remix is played when Oetsu's being hit and it goes into 1v1 sections, aswell as for newest episode for Ishida and Yhwach fights.

Studios aren't restraining their ost just because it is a theme of a character for most of soundtracks, for example Power to Strive which is "Grimmjow's Theme" also debuted in Diamond Dust movie and "Rukia's Theme" [Shikai] is called Senna and it is an ost connected with character Senna from Memories of Nobody movie.