These manga focus on pairs of twins, whether it's solely the twins, or it includes twins as part of a relationship, ie a love triangle, as well as stories about parents raising twins. Twincest included too.
Characters in these stories have suffered the death or disappearance of a close friend or family member. It may be a recent loss they are still grieving, a not-so-recent loss that they are starting to come to terms with, or, in...