Yuu was Chihaya's younger brother. He died in a traffic accident before the events of The iDOLM@STER, and his loss clearly affected her deeply. His death put strain on her family relationships, though the details of how aren't fully explored.
What stands out most is how much Chihaya valued his support. She remembers him listening to her sing and encouraging her to keep going, all while he'd be sketching away in a sketchbook. She's held onto a photo of the two of them from when they were kids—a keepsake that clearly means a lot to her.
Content compiled by AnimeList.moe from publicly available sources.
