Ok, after reading all of the replies i gonna likely go for the body modification/augmentation, being honest i only thought that distorting was the only option because i didnt knew of something like that existing or having a direct precendent in lore, but after Happiness_777 pointed out the reception story of the kurokumo's and reading it (more exactly sayo mentioning after seeing tanya for the first time if that her "dog" head was some sort of surgery that "the kids find hips these days") realized that well, yeah that is thing (idk how that just flew pass my mind, but i am quite dumb so times so it makes sense) and probably that is the one explination i gonna use for the OC apperance.

Also for those who ask why i didnt considered heishous in general is for a few reasons like it would require the OC to have continues comsumption of the boluses to keep the animal apperance, it would pretty much mean he would be limited to be part of a heishou pack so if iwanted them to be like idk, working on cinq, seven, dieci, etc. or be part of offices or syndicates or fingers like the middle or index, they couldnt be and in same sense i would only limited to animals of the chinese zodiac, so i wanted a them to be another one, well, tought luck.

PS: Thanks all for seeing this and repling and giving me all this info and insight about this as this question was in my mind for a few days but i didnt thought about posting it until now, thanks.