I saw a post regarding BB characters being dominants from FFXVI and since I'm a big fan of the game, I decided to make my own. But that post was deleted so I fixed it a little bit and then offer some explanations based on my research.
Dominant of Ifrit (Ragna the Bloodedge) - Ragna already has the perfect counterpart in FFXVI - Clive Rosfield. Both are main characters with dark pasts (losing their family) and red right arms and struggling to control their powers in the beginning and both of their journeys has them accepting the monsters within and becoming stronger for it. Their tragic endings are also similar - Ragna and Clive both sacrificed themselves to save the world. Ifrit would find the perfect vessel in Ragna.
Dominant of Bahamut (Jin Kisaragi) - Yes, we all know we want Jin's Eikon to be Shiva. But there's one problem - Shiva in FFXVI historically only chooses "Female" Dominants. Even the previous Dominant of Shiva was a Queen, and among others, all of Shiva's Dominants have always been women according to the Rising Tides DLC so Shiva's vessels are completely "gender-locked". Jin is canonically male, so Shiva won't choose him. But luckily, there's another Eikon that is perfectly suited for Jin in the FFXVI universe - Bahamut the Dragon King. The canonical Dominant of Bahamut is Dion Lesage - a blonde-haired pretty-boy prince of a high kingdom who is beloved by the people and commands a loyal army of knights. Like Dion, Jin himself is a blonde-haired pretty-boy prince (the next in-line to be the heir of the Kisaragi Family) and beloved by the public for being a hero and protector. Also like Dion, Jin himself serves a high kingdom (the Novus Orbis Librarium) and commands his own legions of soldiers. The NOL soldiers call themselves "The Knights of the Blue Flame" so let's call them knights too, and the Bahamut in this universe uses blue-colored flames and some lasers. The Bahamut in this universe is also associated with Light and Order - two things that Jin also has an affinity with (Power of Order and the "Light" to Ragna's "Darkness"). Bahamut would definitely choose Jin.
Dominant of Garuda (Tsubaki Yayoi) - Tsubaki herself already has avian motifs and bird-like features in her neutral state - feathers flying everywhere and has the ability to fly and charge forward in a lot of her attacks. Of course, Garuda would choose her.
Dominant of Shiva (Es) - Es is definitely the perfect fit for Shiva because not only is she a female character (Shiva's preference), but she is the resident "Ice Queen" - elegant, cool and emotionless like cold ice. Her attacks using her weapon is also very ice-like - light blue-colored attack weapon crest, patterns and motifs. A lot of Es's attacks leave ice-like geometric patterns across the arena. Shiva would DEFINITELY love her.
Enjoy! I hope I managed to make these as clear as possible. I'll try to post Part 2 as soon as I can.