Kaijin Mira no Dai 2 Keitai ga Kawaisugiru

"Cuteness is indomitable!" Day after day, the mysterious Mira rampages around, trying to steal the hero's transformation belt. Mira is at full power, having been remodeled by the doctor, but it turns out her new form is that of an incredibly cute girl! Mira, who has been remodeled based on the theories that "a hero won't raise a hand against women and children" and "justice cannot defeat cuteness," has been ordered to make the hero fall in love and to steal his belt. Meanwhile, the hero, who thinks love is a source of trouble, is at the mercy of Mira's cuteness, but he swears he will never fall in love with her. So begins a romantic comedy where justice and evil refuse to yield to each other!

(Source: Akita Shoten, translated)