Sakana's Search For Fellow Thinkers

[alint]

All these people suddenly coming out of the woodwork!

Do you have any specific ideas, @abalint ?

Twins are playing in backyard, one falls down [for lack of a better word] a rabbit hole and disappears into another dimension. Years after the incident the twin who disappeared returns, but they're both adults now. Can they get back to being a family? Or will they be forever estranged?