Made in Abyss Official Anthology - Vol. 2 Ch. 5 - Until The Day We Grow Up (by Sakasana)

[MangaDex]

 

[Zizhou]

Aw, geez, that's pretty bittersweet if you consider that Nat and Riko are never going to meet again, barring some miracle at the bottom, or Nat going full white whistle and braving 7+ layers later on.

 

[Azrapse]

It gives more meaning to Nat's tears when Riko is leaving, since he knows he will never get to see Riko growing up.
And that probably she will never get to grow up at all, given how lethal the Abyss is.

 

[Liquidxlax]

Advice on feelings for things that once brought normal happiness and changed due to hormones would be far more appropriate. Kinda wish I was given advice when "that" occurred or asked my parents. I thought something was wrong with me for a long while...