Free! dj - Ichiban ni Naritai no.

Pairing: Makoto x Haru

From Seabreeze Romance Scanlations:

Who knew chocolate could start a crisis of the heart? Ran begs Haru to help her bake chocolate for Valentine's Day in secret, with the intention of giving them to Makoto. However, Haru realizes that an innocent sister's crush isn't quite the same thing he feels when he thinks about Makoto. Add in Nagisa begging for sweets, poor Rei caught in the grand conspiracy, Makoto thinking he's imposing, and Haru's got quite a mess on his hands! The worst part though? Realizing he's felt this way about Makoto all along.