Mahou Shoujo Pretty Bell

Japanese Title: 魔法少女プリティ☆ベル

English Title: Magical Girl Pretty Bell

Plot
Magical rod "Rin Rod" has been awakened. Pretty Bell is the name given to several generations of young girls who become magic using fighters through the powerful Rin Rod. They are able to summon mythical creatures and weapons to fight against the demon world. When the compatible user "magical girl pretty bell" appears, it always says that the world will be at risk. Milk and Cocoa are angels from the Heavens who protect the rod and support magical girl pretty bell. They are sent on a mission to find the next Pretty Bell and they have come to the town where a compatible user, Misaki Eri lives, while being attacked by an enermy. However the rod didn't point to Eri but pointed to another man. Unfortunately for them, the next candidate for the position is Takada Atsushi, a middle aged bodybuilding muscle man who owns his own gym.

Atsushi, as unlikely as it may sound, fits in fairly well with the position. His physical strength and combat skills are enhanced with the magical power, making him a deadly force to be reckoned with. As wave after wave of demon horde come after the new Pretty Bell, the weird looking hero has to protect the human race.

Why did the rod pick Atsushi instead of Eri? and why there are two compatible users?