One Punch Man Manga Chapter 29
Saitama receives a care package filled mostly with letters praising Genos while criticizing him, which frustrates him when Genos reacts seriously. However, Saitama later receives a heartfelt thank-you letter from Mumen Rider.
The Hero Association promotes Saitama to C-Class Rank 1 and grants him the opportunity to move up to B-Class. During discussions, staff members debate whether he is a genuine hero or a fraud, while Sweet Mask dismisses the issue, saying he only cares about A-Class matters.
Afterward, Saitama meets Mumen Rider—the sender of the letter. They exchange respectful bows, take photos together, and share a meal at a local restaurant.