Nakishi is a special greninja that is a whisperer to both his own kind and reptiles and wants to be an ambassador to both. He has been bitten by a serperior and a feraligatr to try and be friends with but they got a bit aggressive and got bit by them separately but he considers this like a rite of passage that sometimes you'll get bit by ones your trying to befriend so now he wears those scars with honor rather then shame. He put tattoos on both arms that he got bit to show he wants to be friends with them.
With the other symbols on his belly and arms he's befriened those types as he loves and cares for all of them.
Venusaur - a big Venusaur he befriends in a vast forest that the motherly venusaur lives and the hybrid greninjas and she is one big lovely gal to him and gladly lets her nom him and finds her belly relaxing to take a nap in or massage her belly.
Charizard - Nakishi finds this big softie charizard by a river that runs around a molten fiery area and is seen as a big pred with some gigantamax energy flowing through him but of course does go to the full height and he usually wants to be nommed by someone but is too big for the belly and Nakishi tells him that your great regardless how big you are pred or prey doesnt matter and sweet talks him to nom him and smiles and gladly noms Nakishi and Nakishi enjoys his belly like a sauna and feels pleasant
Swampert - Nakishi finds a sweet little swampert that is an excellent swimmer and Nakishi liked how elegant he is and befriends him and admits he always wanted to find a great pred to nom him to see what its like to be inside a belly but his mother is always protecting him that he never got the chance so Nakishi chats with his mother which is a mega Swampert and tells her and assures her that her son would be safe with him inside his belly and is convinced so he gladly goes inside his maw and slides right down into his belly and enjoys being inside but the deal with the mother is that she can nom him after her son is out and safe and agrees to the deal and Nakishi gladly goes inside and enjoys being inside and meditates.
Sceptile - Nakishi finds a fierce tough Sceptile and likes how elegant he attacks his prey and enjoys a good prey/pred that shows how tough or soft he/she can be and befriends this sceptiles and tells him about a time even if your tough and can take down your prey what happens if the parent or someone that cares for it decides to nom you since your in a weak state you need training on how to handle being inside a belly and i can help with that and the Sceptile agrees and noms him and both meditate together outside and inside the belly.
Greninja - course his own kind is no problem being friends with since he has his masters symbol on his back as he loves to be inside his masters belly to train and meditate. But Nakishi finds a beautiful female greninja that has traveled to Hanzo's valley and dojo to train and loves to be a switch like himself and she gets into Nakishi as she goes inside his maw and dives right in and meditates inside his belly and has fallen in love with her no matter if she is inside his belly or outside.
Inteleon - Nakishi finds a good looking inteleon that was on a spy mission in the area and needed a place to lay low for awhile so she wouldnt be tracked or found so she finds Nakishi in the area and immediately become friends and she gladly goes inside his belly to avoid being seen and Nakishi gladly lets her in his maw and belly to lay low but finds it relaxing to stay inside for awhile. After the threat is over the Inteleon decides to stay in the area to live and to be with some of the other water types and others she likes including Nakishi.

Art by

Nakishi is mine

Greninja and other pokemon listed belong to Game Freak and Pokemon Company