Let's Go Karaoke!

Satomi, president of his school's choir club, gets embroiled in a bizarre situation when he's asked by Kyouji the yakuza to give him voice lessons. Surprisingly, Kyouji's quite serious, and diligent in his practice too. As the two spend time together, where will this odd friendship take them. <em class=de-emphasized>(from manga)</em>

Synopsis from Anime News Network