Oyasumi, My Knight

Honami Sonoda suffers from insomnia due to overwork at an exploitative company and the death of his dog Taro. Unable to sleep as usual, he goes for a walk and notices a large dog in a weakened state in a neighborhood park. Remembering Taro, Honami takes pity on him and takes him home, falling asleep next to him. But, when he wakes up, there is no dog next to him. Rather, a mysterious young man... Could he be the dog from yesterday?

(Source: Ichijinsha, translated)