Choku!

Mizuhashi Nao is a 16 year old, who is shy and friendless. He passes his class breaks in the toilet playing games where he won't be bothered. One day an upperclassman appears peaking from above and with a huge nosebleed that covers him with blood. Her name is Serika. Wait, a girl?! What is a girl doing in the boys restroom? And why did she just ask...