Takagami-sama to Aware na Ikenie: Zuika

The god of the land, Murakumo, and his fated partner, Tsubame, a former human sacrifice, enjoy peaceful days filled with warmth and laughter, surrounded by their lively household—their twin children Saika and Shūrin, and Tamaki, a dragon child rescued by Tsubame. However, their idyllic life is disrupted when Tamaki is attacked by a monstrous python while away from home and succumbs to its venom. Desperate to save Tamaki, Tsubame pledges to do whatever it takes, but Murakumo, unwilling to risk harm to the one he loves most, hesitates. As their feelings clash, a rift begins to form between them... (Source: Kaiohsha, translated) Note: Includes one extra chapter.