
but if he does won't that call the wrong "Blood"?

no Rapunzel san told him that Blood is alive but he needs to call "His" name meaning Spider's because Blood and Spider switched bodies so if Ishuca says Spiders name then he would be calling for Blood because ones name is bound to their bodies... i think let me check...
~~THIRTY MINUTES LATER~~
ok so "the body is bound to your given name" which is the name your parents given you but "the soul is bound to your TRUE name which is the name that only you and Creator knows." i know that this sounds weird but makes sense for this manga.
I love this story so much! The inner monologues of conflict are so deep and interesting. Ishuca has such deep desire for him to be with Blood forever and here all I'm thinking is, "when are they gonna bang already?!" I'm the worst!
Ishuca call for your Blood!