Rin, a 22-year-old man, grapples with two significant dilemmas: an insecurity stemming from a peculiar birthmark on his buttocks and unrequited feelings for an older woman who perceives him as a younger sibling. Since a childhood incident at the age of 7, Rin has harbored deep embarrassment about his birthmark, shunning any intimate exposure. However, his perspective shifts when he discovers that this mark might wield magical influence over women. Will Rin overcome his hesitation and harness the power of his birthmark to alter his fortunes in love?