Manga by author Kitazaki Taku

"Progressive Rejuvenation Syndrome." This is an extremely rare disease causing the inflicted person to gradually become younger. The main character of this story, Munenori Agawa, is the only person that could save Rena Amami from this odd disease. Agawa's saliva is the only thing that can halt the disease from making Rena younger, so they must kiss everyday in order for her to survive. This causes an immense amount of conflict and drama between Agawa and his new girlfriend, Sayako Asou. This triangle relationship story tests the capabilities and limitations of human love.

Description : 22-year-old Rin has two major problems: a complex about the tattoo-like birthmark on his butt and a crush on an older woman who thinks of him as her little brother. Rin hasn't allowed any woman to see his naked bottom since an incident when he was 7, which firmly entrenched his shame about his birthmark. When he finds his birthmark may grant him mystical powers over the opposite sex, will he finally be able to use his butt to his advantage?