There was a number 13!?!? - Haikyuu

Alex was someone invited to play in the karasuno boys volleyball team a year before he started school, but after arriving back from a losing game, someone slips up there words and no one has seen or heard from Alex since that day.

What happens when the group of first years, and coach ukai found out about this number 13, and what lengths will they go to get the boy back to karasuno and be the number 13 he used to be, And how will they get the others in board in their mission.