Mind Game

Nishi has always loved Myon since they were little. And now as adults, he wants to pursue his dream of becoming a manga artist and marrying his childhood sweetheart. There's one problem, though. She's already been proposed to and thinks Nishi is too much of a wimp. But upon meeting the fiancé while at her family's diner and accepting him as a good guy, they encounter a couple of yakuza, only to have Nishi grasp a certain revelation. And, with his newly acquired look on life, adventures abound as he, Myon, and her sister, Yan, escape the yakuza into a most unlikely location where they meet an old man...

Synopsis from Anime News Network