I think this SCP would have been fine without the "message" on the last page. Like, we already had Cactusman, self-proclaimed superhero whose head is a cactus. No further explanation needed for that one. This could have been similar.
No major issues from what I can tell (although "Namekawa-san" in the bottom panel on page 2 is formatted a little weirdly and missing a hyphen), so good work!
So, ignoring the little sister thing, I actually like the theme of this manga.
"Stop assuming basic social interactions means a girl is into you, you lonely fucking weeb."
It'd be nice if more romcoms touched on this.
Well, that got dark quick. At the same time, there should really be no need for "creating" one. Just find some trailer park as the old child is about to turn 14, and 204-1 is bound to find some child to attach itself to. If not, well, nothing of value was lost.