Is Chance Triangle Session hentai?
English title: Chance Pop Session
No
Rated PG-13 (Teens 13 or older) on MyAnimeList and not tagged as Hentai.

TV · 2001 · 13 episodes · PG-13 - Teens 13 or older
Drama, Idols (Female), Music
This anime is based on a 1999 radio drama about three very different girls: Akari, Yuki and Nozomi; going to see the concert of top pop idol Reika and by going to see this concert their lives are greatly influenced by it. Akari was raised in a very religious background, she is bright and cheerful and a big Reika fan. Yuki is an independent girl who ran away from her home in Hakodate. She is working in the concert hall of Reika's performance. Nozomi is the daughter from a wealthy family in Kobe. She's got one of the VIP seats at the concert. The three girls are so inspired by Reika's performance, that they all enroll in the Akiba music school and endeavor to become pop idols themselves. (Source: AnimeNfo)
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