The Flame and the Tempest (Muramasa x Rimuru x Ciel)

Translation:Word (Microsoft), there are probably errors in the masculine and feminine pronouns.

Senji Muramasa woke up in an unknown world, enveloped by overwhelming mana and an eerie calm. Without a Master to guide him or a clear mission, he decided to continue with his life in the same way he had always done: forging weapons and facing each day with the mettle that characterized him.
In his refuge in the middle of the forest, his routine was interrupted by the unexpected appearance of a girl of short stature and bright blue hair, who introduced herself as Rimuru Tempest.
Between the heat of the forge and the glow of a world filled with magic, the blacksmith and the leader of the Tempest Kingdom began to forge a bond that would change their destinies.