Master-Servant Vow (主従誓約 Shujū seiyaku) is what exists beyond the Master-Servant Contract.
The master servant vow is the deepest subordination one could give to one’s master. It’s the ultimate form of master-servant relationship, which could only be reached between a master who’s prepared for their subordinate to belong completely to them, and a subordinate who could vow their heart and body entirely to their master.
On the other side of the unbelievable power that came with it, is a forbidden relation that could not be erased. Among those whose souls are tied together by the master-servant magic, there aren’t many who could successfully reach the vow. It’s always been seen as nothing more than a legend or fairytale.
The vow ties master and servant together forever, and significantly boosts the power of a master as well as their servants. There are several conditions required for changing a Master-Servant Contract into a vow:
- The original contract has to reach its maximum possible state.
- Servants have to be willing to devote all of their heart as well as their body eternally to their master