Mr. Mega Man Volume 2 : Volume 2 by Yuushi Kawata

When Mega Man grows up, he must face his greatest challenge of all... life as an adult!The battles with Dr. Wily are in the past, and Mega Man has grown up in a peaceful world. Now spending his days as a dentist, Mega Man has begun to notice a rise in strange, robot-related incidents. As a result, he must once again use his great power to protect the world and uncover the mastermind behind this mystery.
Binding: Paperback / softback