Mienfoo first appeared in Across Skyarrow Bridge!, where he was seen training diligently on Skyarrow Bridge. An old lady informed Bianca that Mienfoo trained there every day in order to strengthen himself, as his previous Trainer had released him for not being strong enough.
Bianca decided to have Mienfoo train her and her Pokémon to, although he refused initially. However, sensing that Bianca's Pokémon wished to become stronger, Mienfoo decided to train them. Together the three Pokémon began training together and powering up their moves, forming a strong bond in the process.
At the end of the day, Mienfoo decided to stop waiting around for its old Trainer and asked to go with Bianca, under the pretence that he wanted to continue his training with Tepig and Vanillite. Bianca, however, recognised that he really wanted to stay with his newfound friends and accepted his request.
In Challenging a Rock Solid Figure!, Bianca used Mienfoo in the Challenge Rock Contest. During the contest, Mienfoo learned Aura Sphere and used it to destroy its rock, allowing it to win the contest. After the contest had finished, several Black Belts offered to trade their Pokémon for Mienfoo, but Bianca refused.
Bianca left Mienfoo at home when she left for Sinnoh.
Mienfoo is a very serious Pokémon who rarely shows any emotion. Having been abandoned by his former Trainer for being weak, Mienfoo sees strength as everything, training hard every day to prove himself to his old Trainer. He also seems willing to help other Pokémon, as seen in his decision to train with Tepig and Vanillite. Mienfoo also sometimes covers up his emotions, pretending initially that he only wanted to go with Bianca so he could continue his training of Tepig and Vanillite, although Bianca immediately saw through the ruse.