Wow! Thanks for such a thorough reply on the 4 Beasts! I'll check out the story recs later!
For my theories, they are very out there so I feel a bit embarrassed to share them (especially with the upcoming event ready to debunk them lol), but your reply has motivated me so here we go!:
First some realistic thoughts: I think Ibuki's storyline will heavily involve Nice. Nice is the only person Ibuki calls by their first name and without an honorific(Yoshihide), though he does try to use Na-san in front of others. It could just be the American influence, but I feel like Ibuki's respect yet casualness hints at something more.
I don't think Ibuki will officially join Akatsuki, but his situation may be similar to Kohaku(my favorite Enstars character who Ibuki has a lot of similarities/parallels with, probably why I like Ibuki so much). So he'll have his own unit, but also be a like a sixth ranger to Akatsuki, sometimes participating in their events.
The following is heavily delusiona...
Anyways, the last name ties in with who I think will be Ibuki's unit mates. While Ibuki has a high solo potential, story and card-rotation wise, it would be easier if he had unit mates. I think his unit mates will eventually be NEGI and Nice, with the unit's theme being an "international" unit + "playing tag/鬼ごっこ." There is no basis for NEGI besides liking her and feeling like her story could expanded + she was hiding out in the US. For Nice, this is pure unsubstantiated speculation, but I think Ibuki is chasing after him, similar to Canis Major (Sirius) and Lepus (Arneb). Perhaps out of admiration or to have Nice return to being an idol?(He is pretty young for a famous retired idol, being the same age as Rinne). To do so, Ibuki will be "tagging" or collaborating with other idols until he finally "tags"/catches Nice. Or something lol!
I tried to cut the amount of text to just the main points, but it was still a lot huh... though I have zero expectations that any of this wil...