Open The Door To Your Heart(2001)

Aiteru Door Kara Shitsurei Shimasu yo

Honda's life is anything but exciting; he works as a public tax accountant for the city. Honda and Shunji are cousins, but when Shunji's parents passed away, he was adopted into Honda's family. Yet, Shunji went missing for 10 years. Now, when Honda is reunited with his younger brother, his life is flipped up-side-down! What do they have to say to each other after all these years?

(Source: Juné Manga)

Note:
- Includes two extra chapters
- Includes the side story "Komazukai no NIkki (小間使いの日記 | Diary of an Errand)"