a seal is not a bloodline, I never even said it was, a seal is something crafted and it can help store, restrained and even power things,a persons and creatures. Tsunade created the seal so that she can store chakra in it and help her with her medic-ninjutsu, but it requires extreme chakra control to focus on said spot for it to store itself, something that Shizune wasn't able to do but Sakura was. The moment Sakura started storing chakra the seal should have appear, since she's storing it in it. I notice you continue to not answer the question but only answer what the seal does, again, How do you store chakra on a seal that was never there? The seal is the one storing the chakra, not Sakura or Tsunade but the seal. When Tsunade uses it, it banishes but the moment she starts to store again it returns.