Can somebody explain what did Gale -the redhead boy- invent in the past? Was it the seal to create door?

ack the hell i meant to like

I think that Gale invented the seals where you can't see or know the demons who's forming a bond/contract (I forgot the name sowwyyy)

In the beginning, Cain is really confused when seeing a seal without the name of the demon, and I think Gale is referring to that?

(I may be totally wrong bc I read those last chapters while studying for my finals lmao and wasn't paying that much attention)