Alright, let me lay it out how the entire seires of seals works. It's like this. Itsuko already has a seal that stores venom inside her, however right now it is a huge liability because there is nothing containing it. When she uses jutsu, the chakra venom seeps into her own chakra network and poisons her, pretty much making her unable to use chakra for fear of dying.
This seal will make it so that instead of infusing into her own chakra network, the venom that leaks out when she uses chakra will be captured by the two seals on her hands(this seal). As long as she doesn't over do it, and limits her chakra use to keeping the seals below capacity, she will have a way around her own chakra venom, and can utilize it.
It is on her hands because yes, this is what stores the amount of venom she is able to use while fighting. The venom is made by the spider seal, and stored in her containment seal until use. This limits how much venom she has access too over all, and while 80 may seem like a lot of C rank, this number is not going to change when she's S rank, so it will be a limiting factor for her.
So, it goes like this. Itsu uses a jutsu and spends 20 chakra. 20 points of chakra venom leak into her system, but are captured by the containment seal. She then has 20 points of chakra venom she can put to use with, for example, her gentle fist style, to inject it into other people. The actual act of injecting the chakra is going to be defined by jutsu I will make before long. OF course, if she can't actually manage to lose the chakra, the seal is going to build up and build up until it hits capacity.
She will, of course, have other ways to rid herself of the chakra before it becomes a problem to her again.
Oh, also, no! You didn't see anything about activation, but the word automatic was in there a couple times and seemed to make you uncomfortable. So I removed the word, without changing anything else.
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