Märchen Ouji Grim

Isobe Tatsuhiko has a huge crush on his hot, popular, childhood friend Shirayuki. To his surprise, she's agreed to go on a date with him, provided he plays a part in the success of his baseball team's next match. This sounds almost impossible to the benchwarmer Isobe, until he finds an unlikely source of help. The enthusiastic, vaguely homoerotic Prince Grim from the Fairy-Tale World has traveled backwards in time to help his future best friend win the girl of his dreams! The stakes are high, since Grim knows that losing Shirayuki will eventually cause Isobe to go on a rampage and destroy the Fairy-Tale World...

(Source: Mangahelpers)