From what I understand so far, they vowed to Stagnate that as long as their attachment to high king’s seal is their most important feeling, they won’t become Stagnate’s underling.
So it’s not like they don’t want to keep the seal up. Will become more and more important to them until the existence of high king’s seal is not their number one priority anymore (maybe number two?). The moment their love for Will is greater than their attachment to the seal, they broke the vow. Hencewhy Stagnate’s echo appeared to pick their soul and said thanks to Will. Because of him, Blood and Mary broke the vow and he can make them his underling.
Both Mary and Blood have compassionate mind, so it’s understandable hard for them to manipulate their own feeling. Gus, on the other hand, is more rational. I think he knew Blood and Mary’s feeling and afraid they’ll break the vow, so he tried to kill Will in earlier chapter. But even he’s wavering. I feel from that point, Gus tried to keep his distance to Will.
That’s what I understand from last chapter. Wow! I wrote such a long reply!
(๑•ㅂ•)و✧
Makes much more sense now! Thanks for taking the time to write this :)
Love your explanation! It makes me more understanding the story flow. Thanks
Why would blood and Mary lose their connection to the seal? Wouldn’t they want to keep it up for will while he’s out seeing the world so he’d be safe from the demon king.... at least 100 years or something they sent their baby out then agreed to die again leaving him unprotected and releasing Satan all at once.... ok