Vampeerz, Volume 5 (manga)

As the school year progresses, it is now time for a field trip. And this one takes Ichika and Aria to the mountains for a class camping trip. Out in the woods and nature, there is plenty of time to get to know friends and partners on levels that are much more intimate than what is commonly seen in normal society.

People have to work together to survive, and in this case with an accident threatening their lives that is at a premium. And then we get a long flashback to Ichika's grandmother's teens. How was her relationship with Aria? Were her heartstrings also pulled tight?!