Sumire may be dumb and debased, but Souko is a true degenerate. Her Sumire-based inferiority complex is sad and pitiful. Maybe once she sees how Sumire lives, she'll feel a little better about herself?
I just realized where this setup is going. Yuusei is a super fan from their idol days. He's going to give Souko some poignant compliments about her time as an idol. Which will stab her inferiority complex right in the heart, extreme validation. It's the perfect storm for her to fall for him.
Gloomy hentai cougar, get.