GREAT QUESTION!! (and thank you<3)
one of the great ncej dichotomies is how differently they show their affection - nico tends to be super open with his while euijoo tends to obfuscate (hence there being more obvious nico_simping moments) BUT ofc that doesn't mean euijoo doesn't have his fair share!! brief list off the top of my head:
1. i always go back to tingle salon because i feel that euijoo was extra open/comfortable in that video, esp in the second half! here's a timestamp: https://youtu.be/48k9IIjgHlQ?t=2173 the way euijoo looks at him, looks away, looks back, looks from under his eyelashes, ETC. so in a headcanon-y sense i really think that euijoo likes looking at nicholas and tends to hold himself back from looking too obviously...
2. EUIJOO'S BIRTHDAY LIVE where he does aegyo right after nico leaves and then when he comes back he's like "did you see my aegyo?" and when nico says no he pouts extremely cutely. and then nico says "you're cute no matter what you do" :/ https://x.com/907x709zip/status/1699793523674128848 Hence i think euijoo does actually enjoy being babied by nico in a sense. Hence why i have a disease that makes nico call him baby in all of my fics. LOL (there's also another great moment from this same live where euijoo reaches for nico's hand, doesn't let himself grab it, and then sighs. To Me all of euijoo's ~simping~ is wrapped up in self-denial! which is what makes it so delicious!)
3. tbh the sheer joy that euijoo gets from learning languages from nico and how proud he looks when he gets it right - i think euijoo admires a LOT of things about nico and one of the easiest + least revealing ones for him to express his admiration for is the language thing. he always looks impressed when nico shows it off, nico always looks proud when euijoo follows.
4. i was going to stop at 3 but i just remembered this https://youtu.be/71-4X0z_y58?t=164 where euijoo (+yuma) are going through nico's taiwan photoshoot magazine and euijoo was like... really into it. LMAO
5. actually last thing https://x.com/ejkkinoe/status/1797832817507979509 when kei said that euijoo hugs nico in his sleep :/ either it's his unconscious self reaching out for him or he isn't entirely asleep when he does it. and tbh idk which is worse