It seems like Suzakutai and Genbutai were real military units during the
Boshin War (sometimes the Japanese Civil War) from 1868 to 1869. They were two of
four units from the Shogunate's Aizu Domain and the other two were Byakkotai and Seiryuutai.
I'm not sure which Sentai the manga might be parodying/referencing though (if it even
is Sentai).
Anyway, Genbu, Seiryuu, Suzaku, and Byakko are the
Four Symbols or the Four Guardians.
Each of the creatures is most closely associated with a cardinal direction and a color, but also additionally represents other aspects, including a season of the year, an emotion, virtue, and one of the Chinese "five elements" (wood, fire, earth, metal, and water)
Here's the table of their associations from Wikipedia:

and their depictions from the Megami Tensei multiverse lol





Yeah, pretty much it. As always, let me know of any errors or points of improvement. Thanks
