Gil is dying. Gil isn't supposed to die. They've almost won. Why did the idiot have to take the blow? Oz was a Chain, he'd have been fine after a day, but stupid stupid Gil had shielded him and was dying for it.
"Don't you dare die Gil" he orders, even knowing it's useless.
Gil confirms his fear. He can't lose Gil. His hopeless idiot belongs to him. He's already lost rejected sent away will never see his Alice. He can't lose Gil too. And even though he knows Gil will return in a hundred cycles it would be impossible to find him. Nothing even guarantees that anything of his Gil would be left. —But maybe there was a way.
He summons his scythe, and unhesitatingly cuts his hand. With a contract —even a short one— the rules would change.
He offers his blood to Gil, and feels his servant's tongue lick the cut. The contract is made, and he grasps Gil in his power, (gently, so gently) his full power far too much for even a Baskerville. But this is Gil. He controls himself.
He wraps himself around Gil, the small fraction of his power that the human could handle, and lets himself taste Gil's soul. The moment seems to last an eternity. Gil is like a fire in his grip, one that won't burn him, and so small and fragile in comparison to Oz, but stubborn and strong, even wounded and dying as he is, with a broken rib puncturing a lung, and a crushed throat, only alive this long because of Baskerville healing. He feels Gil's shock and fear, swamped in his power as Gil is, power no human could hope to contain or control he knows, and how much of Jack's fall was his own fault?
He smiles. I have you; he soothes the bright, fierce devoted warmth that is Gil, embracing him more firmly. I'll protect you next time.
Gil flickers out, the soul escaping his grasp and Oz tucks the memory of that moment close to his heart until they meet again.
The first time he finds the soul again Gil is female, and Oz would tease him so much, except Gil doesn't remember him. Gil isn't fully happy, but by the time Oz finds Gil, Gil is content, married and a mother. There is no place for Oz there. Gil has a good life. Oz stays anyway, and watches from the shadows. Gil dies young and of disease as she begins to remember something of him. It's agony to watch, but disease is no enemy Oz can fight. He watches over Gil's children until they're grown. Then he leaves again.
The second time Gil dies at ten, victim of an accident, as he began to remember Oz. Oz was too late, and finds him as he dies again.
The third time Gil is female and noble and Oz becomes her knight. She dies in an ambush, remembering him at the end, and Oz grimly realizes the pattern he sees. He feels cold satisfaction as her killers fall to dust before his power. Nobody hurts what's his. He brings her body back to her family and vanishes from the human world, waiting once more.
The fourth time Gil is male again and this time looks just like he did when he was Oz's Gil, and Oz allows himself to hope that this time will be different.