Pretty Haru 

As children, Lee Haru and Yun Dong-Ha made a promise, one to become a famous baseball player, the other a ballerina. When Lee Haru departs for Russia, they both decide that when they meet again they'll become a couple. Fast-foward several years, and Dong-Ha, now a feared deliquent, is excited to find out Lee-Haru is returning to his school. Expecting to meet a gorgeous, skinny ballerina, he is rather dismayed to find out Haru hasn't exactly turned out the way he expected. From Baka-Updates