Onegai Muscle (お願いマッスル)

“Onegai Muscle (お願いマッスル)” is the opening theme of How Heavy Are the Dumbbells You Lift? and is performed as an in-character duet. Fairouz Ai sings as Hibiki Sakura, while Kaito Ishikawa answers as trainer Naruzo Machio. Its call-and-response structure turns exercise vocabulary, muscle names, and shouted encouragement into an instantly memorable chorus. Hibiki voices her wish to get fit; Machio responds with exaggerated enthusiasm and the commentary of an unstoppable instructor. Bright brass, a marching pulse, and group chants make a workout routine sound like a stage performance. The song captures the anime’s comedy without treating exercise itself as a joke: effort matters, small improvements are celebrated, and the gym becomes a social space. It also establishes the central dynamic immediately—a beginner with recognizable everyday goals paired with a trainer whose passion for muscles overwhelms every situation.