some refs for kame and femkames shackle marks,

not naturally occurring they're from a curse put on him from long ago to exert control over him.

Resembling shackles they appear on his neck, wrists, ankles, tail base and just before the bush on his tail, same positions with femkame.

when in Femkame form some of them shackles break the ones on her ankles neck wrists all break, the one at her tail base doesn't break completely and the one at the end of her tail stays complete.

magically attached to the neck shackles is a leash, usually not visible to mortals if you manage to grab it you can exert full control over him basically making him do whatever you want to. It has less of an effect on Femkame due to the broken shackles so it requires a bit more will force to get her to do what you want.

it is possible for kame to fight against the leash but to do so would end in him killing the holder. so usually if he knows that the holder doesn't have malicious intent he doesn't fight.

fem kame usually just punches you in the face.