They're Lion/Tiger hyrbids so they are very ferocious and powerful in terms of land based summons. They seem to be pretty suited to close quarters combat. The overall theme is Greek, AND MOST OF THEM ARE ARGONAUTS. Except for Sinbad who's a sailor. You could also make the argument that all of them are in some way affiliated with the water or a ship. Achilles sailed to Troy, Sinbad was a famous sailor, etc.
*arrives at the base of a tall mountain in the Southeastern Borderlands of the Land of Earth*
Bad description. Ligers are the result of male lions and tigresses mating, producing a Liger. The inverse ( a male tiger and lioness ) produce a Tiglon. Ligers grow to be the biggest cats of the animal kingdom, while tiglons are generally smaller than both lions and tigers. Ligers are very powerful by comparison and despite their big size, quite agile. Because of their large size, most if not all came to favor Taijutsu or Kenjutsu, allowing them to use their size to their advantage. They also have a Greek culture they are known for, naming themselves after various Greek Heroes, their abilities often matching their mythology counterparts. And yes, most are Argonauts besides Sinbad and Icarus.
Anyway, it appears we're here.
*looks up at gigantic mountain* yeah, you have to climb that by hand, no chakra enhancements. The spirits are always watching and this is your first trial. Climbing the mountain to show your determination. When you make it to the top, you'll be ready to move on.
*summons liger and scales mountain quickly, disappearing into the clouds near the top*