Danshi Koukousei o Yashinaitai Onee-san no Hanashi

After Minoru Soramoto's parents ran into crippling debt and left him to fend for himself, he finds out that they also left him in the care of his neighbor—a stunning, coddling, and mysterious young woman who is obsessed with him. Only one thing is certain: she loves him. In fact, she adores him with all her heart, insanely so, and beyond her means… but, why? What has Minoru done to be loved that much?!