What, exactly, does Masturi bring to the relationship that Harumin wants?
I too had been wondering about all the love for Matsuri—I have a hard time forgetting the sociopathic sadist we were first introduced to. And in real-life matchmaking terms, you’re right—forget about a relationship, in reality Matsuri’s type is barely tolerable to be around. A Harumin in our world could certainly do better.
But in the story it’s easy to explain. Most of the main characters in the story range from being significantly inconvenienced to being totally paralyzed by obligations/expectations/familial oppression, or other social pressures. Shirapon was brought up forbidden to ever laugh for god’s sake, and even cheerful Yuzu is burdened by the stresses inherent in her secret love. Matsuri is the only one who seems to be free to do and say what she wants, and ever since her abrupt surrender in the war with Mei and her subsequent characterization makeover, she’s been at worst a bit of pest, and at best an important truthteller.
So yeah, in real life I steer well clear of the Matsuris of the world, but in this manga, even though she can be annoying, she consistently brings a bit of fresh air to a fairly claustrophobic social world. And Harumin could use that fresh air nearly as much as anybody.