Perhaps D is injured while protecting a village or someone he cares about, and a fellow hunter, who has a secret crush on him, comes to his aid. As D is bedridden, their relationship deepens in a Yaoi - like way, with tender moments and growing affection. For example, the other hunter might bring D food, clean his wounds, and they start to have deep conversations that reveal their feelings for each other.
It could be that D is poisoned by a vampiric curse which is slowly weakening him. A mysterious male figure appears, who has some knowledge of the curse and tries to help D. During the process of trying to find a cure, they form a bond. This bond could turn into a romantic relationship as they face various challenges together while D is in his weakened, injured state.
One possible plotline could be that D is injured during a battle with a powerful vampire, and a male character who has feelings for him takes care of him. This could lead to a developing romantic relationship between them as D recovers.