Onegai Teacher!

a story mainly revolving around a tight-knit group of friends in high school and how they cope with several life-changing events that are never too far off from intimate relationships. The main character is a boy named Kei Kusanagi who suffers from a very rare disease which causes a comatose state referred to as a “standstill“ whenever he is under severe emotional distress. From OtakuZone.com: Kusanagi Kei, a high-school student living with his aunt and uncle, has an encounter with a female alien. This alien is revealed to be a new teacher at his school. Later, he is forced to marry this alien to preserve her secrets. From there, various romantically-inclined problems crop up repeatedly. (Source: ANN)