
I don't think they formed a contract yet since anna said mitsuru shouldn't be tied down to anyone including himself. Aside from the fact he treasures mitsu not just being a nectar, he is scared IF mitsu was to form a contract to other biter and he himself can't control his natural instinct anymore since he bit him twice already + his love to mitsu and bite him and will die.
Since the contract is done if the biter gives their blood to the donor/nectar but the author didn't show us anna gave blood to mitsuru both times when they were children and when they had sex though anna drank more than a cup.
But then there's this erasing memory during breeding period thing but i doubt anna would do that to mitsuru. And the amulet repellent for biters including anna himself.
I'll give this 5 stars just bc of seme's hair.