I saw a lot of people hating on UM1 as if he was some good guy that was meant to have a soppy backstory. Instead for me, I see a decent villain who was a bitter and jealous soul driven to extremes by his own negative emotions. UM1 wanted to become someone great but couldn’t step out of the shadow of the anomaly that was his brother. And in the end, we see he valued his brother even if he hated every fiber of yorichi, hence why he held on to the flute because to him it became his “it’s like you’re with me brother” thing.