DihRisza

All of this is what I think happened:
She eloped with a guy, they probably ran for their lives when the lightning struck leaving only their shoes but because the brother only looked the shoes he developed a trauma.
I also believe the sister boyfriend is probably the older brother or relative of the seme and sometime in the future he will tell the uke that he (seme) is still in contact with him (the boyfriend) and that his sister is okay

Eu reread like 3 times to try to see if i spot a body but couldn't. Guess he being a child and liking his sister was to much. Thank you for you explanation!!