DASD-383 One day, my beloved older sister decided to marry a creepy boyfriend. Mizuno Asahi

Asahi, her step-sister, is working hard to raise her younger brother, Yuuki, to be a respectable member of society. Meanwhile, she recently found her first boyfriend, Iwata. He's ugly and creepy, but Asahi thinks he's a wonderful guy. However, just like his appearance, his personality is twisted. Asahi abandons her brother for the sake of false happiness.