I was most displeased when Lillie still called her nebby after I caught it. I enjoy naming legendaries stupid things like "mrbiteyface" the rayquaza and "cuddlemuffin" the groudon (let's not forget Buttmoose the Xerneas for wondertrade purpose)
If I had the games(Arceus dangit, Mom!), I would probably name my Solgaleo/Lunala Nebby for obvious reasons(GET IN THE BAG!). If I didn't for some reason, I'd name Lunala Princess Luna and Solgaleo Simba. Both because reasons.
For me, I only nickname Pokemon that I'm going to use on my team. (Except this one Dunsparce which I named Teapot in tribute to you know who @Teapot) Since by this point I didn't have a sixth member nor a steel or psychic type, I brought Solgaleo into the team roster. I decided to name him Solion, a pun on his name and the animal he's based on (a lion).
Solar Nebby? That's pretty amusing. I, of course, had to name my Lunala Nebby because it didn't seem right to change it. My other Neb-er, I mean, Cosmog, I named Moses because I'm going to send him to another world and have him come back to me completely changed. XD
I named mine Jack O'Neil. I'm a big fan of Stargate SG-1 and going to the Ultra Beasts world is like going through a Stargate and Jack was kind of the lion of the show for the first eight seasons. I also named Cosmog Cam Mitchell.
In Pokemon Sun I called my SolgaleoNebby
In Pokemon Moon I called my LunalaNebbie
Solgaleo is actually the "male evolution" of Cosmog/Cosmoem, and Lunala is actually the "female evolution" of Cosmog/Cosmoem according to the Pokedex. Yes, I know they're genderless, but I'm stating from the Pokedex, not my opinion. So, I called SolgaleoNebby, because I loved Nebby, and wouldn't just change his name to something like Sunstrike. Lunala got the name Nebbie, I didn't want to copy Nebby again, and I knew this male/female thing so I called it Nebbie which sounds more feminine, not offending anyone if it's a boy name or something.
Underline = Something Pokemon Italics = A Nickname
I don't actually have one, but a good name for a lunala would be starla, right? Because on the cover of the games it's in the night sky- and there's stars in the sky!!!!! I'm still not sure about solgaleo. How about sunny?
I initially didn't nickname my Lunala, but in November of last year I nicknamed her Faith, because when Cosmog evolves into Cosmoem, it has to put all its faith in its trainer to protect it since it does not and cannot move.
That makes sense, right?
I was never very creative with names, lol. My Lunala was Nebby, however. When I got a Solgaleo I named him Sole. And then in US/UM my Lunala was Nebula and the Solgaleo (which I didn't get until a bit after the Let's Go games took over, I got it from a friend who planned on quitting the game.) I had it nicknamed Nebulous before he traded it to me.