Only started reading this because this chapter popped up in the feed (and it's Seo Kouji). Was alright, but a little too predictable, but that's just how old manga is.
Pretty sure these are the two main characters, not the son and a girl who suspiciously looks like the mother. It's a "What if" timeline where the two main characters meet many years later without any supernatural phenomena. What a flashback to this old entry.