Isekai Mahou Shoujo Radical☆Haruna

Haruna, a magical girl who fought against evil to protect everyone's smiles, is suddenly transported by a mysterious magic circle to an unfamiliar parallel world. In this world—where the concept of "Magical Girls" doesn't even exist—the Demon King, once defeated by a legendary hero, shows signs of resurrection. As a result, massive swarms of magical beasts have begun to overrun the land. Upon learning that evil is robbing the people of this world of their smiles too, Haruna stands alone against a massive tide of monsters threatening to wipe out a village. No matter how many wounds she sustains, or how blood-stained she becomes, she never stops smiling as she eradicates the darkness. Slowly but surely, the name of the "Magical Girl" gets etched into the history of this parallel world.

(Source: Kadokawa, translated)