Jeez a lot of ungrateful people. There's not much time to share characters' past so I think this is the only time we get to know about Obanai.
This is just my guts telling me but I think this pair will join their friends in heaven. But I'm okay with that though, as long as they go together until the end.
I think Obanai is the last character we should know out about the past. Who else who doesn't get the chance to tell their flashback? I guess almost every one already share their stories.