Nervous anon back... I hope you don't mind me going anon when I'm talking so much. But Im here since you said you would like to hear my Nms reaction to X and how I imagine them interacting! For the sake of things, I'll call my Nm 'Moon' (which is a nickname only closest to him use) just so that i ease up on the confusion of which Nm im talking about.
For starters, the reason why Moon is actually well behaved is because after the incident, while he was still a rage filled confused child, someone found him and helped him along the way. He wasnt alone through his corrupted young years. And so even as the path to be truly healed is still very long, Moon actually has a motivation and a support to get through it. Even as now in his adult years he isnt that much in contact with that person anymore.
Thats for some basic backstory just to know some context.
If Moon met X in a similar situation as in which you described Swan, he would probably first be very shocked and uneasy. (In his world, X would be considered a deity, and with powers similar to him he would first think X is a threat) But when he would realize that X is even more scared of him that Moon ever could be of X, (probably also backed in a corner staring) he would try to make himself smaller to make himself seem a lesser threat. He would hide his tentacles, slump down a little to not stand in a strong position, and maybe possibly even getting on his knees in front of X when the child still isn't calming down.
Most likely he would be forced to be the one to break the awkward silence full of tension. As I dont think X would want to say something to him. Moon looks awfully a lot like your Nm, which would probably make X more uneasy. What might confuse X would be the fact Moon is still wearing the crown that once belonged to his younger self, which might or might not interest X enough to actually try figuring out what this version of Nm is.
Moon is not a people lover, quite the opposite. But I think what would make him want to help/connect/get to know this kid, is the similarities they hold. Moon isn't fully his past self, he and the Moon that existed before are and aren't the same person. Hes more of an extension of that old prince of negativity, and so he would feel closer to X than to X's Nm in a way.
And so, if he did manage to eventually win a tiny bit of X's trust, I think he would take him to his castle (if X would not straight up refuse.) and show off the fascinating thing he found to his henchmen. Who would definitely love X straight up. Like, this kid is awesome. A little uneasy, but awesome. (Moon and his henchmen do not have a friendly relationship, as Moon is a person who doesn't want much attachment. They do have mutual respect for each other. Theres still a big power disbalance that is an issue, but Moon doesn't abuse them)
Moon would not want to keep X in his castle though. He doesn't think its a place a child should be at, and he also doesn't think he is capable of actually being someone to X in any way. (He isn't really. Still healing, not healed.) So if no one would come take this kid home (home only counted as safety. If hes aware of Nm, hes not amused and doesn't want the kid to go back somewhere unsafe) he would most likely go to pass X over to either the other deities, or Core. (Which would funnily enough result in X probably ending up with Ccino too. This Ccino is a bit different, but not bad at all.)
X staying with someone else would not stop Moon from trying to get to know him, he would visit, offer to show him around and maybe even teach him a thing or two if X is interested. Overall I think Moon would grow attached to X a lot. And so would his henchmen. The good thing about Moon is that, he knows that hes messed up in a way. Which would bring him to try to get better even more, just so he can actually be somehow a friend to X. It would take a while, but I think they could work out as great friends. If not actually getting close enough for X to actually see Moon as a parent of sorts.
I did focus mostly on how Moon views X in this, but that's mainly because I don't know X that good. And I could never make his reactions accurate enough. If you want to say how you think X would react to this version of his father, I would very much love to hear that. But no pressure at all! I hope I didn't yap too much... And that you somehow like this. Again, have a great day/night!! I love reading your comic and I love X.
(I might even think of how Moon would treat X if it was HIS X. Which could be interesting)
Love love the concept, and if you think about that in the future i would be happy to hear it!
Regarding X, i personally do think he would end up with either Ccino or Core (all paths lead to them lol) but it's mostly because of a small detail i've shown in the comic before
Nightmare does make himself smaller and less intimidating to speak to X (for example, the shoulderpads being fully gone and the outfit being more laid back in this part of the comic where he's teaching X how to read)
If he doesn't it's usually for a reason (like the flashback where they're talking about Horror)
He wouldn't trust Moon based on this, and less so around the castle (as X's story implies being trapped in it)
I do agree that with some time he might warm up to Moon though, he's always wanted a father after all, and if there's someone willing to be he won't say no
