The man made of iron and the will of fire.

Toad Skywalker doesn't have a sacred gear or any kind of magic which suits Rias and her peerage just fine. After a fallen angel attacked him, he was fatally injured. His heart was the most injured. Rias did everything she can to save his heart but it was no use. She noticed a blueprint for an arc reactor and decided to contact a scientist in the underworld to operate on Toad, the scientist agreed to perform the operation and it was a success. Now iron man is born with his own harem starting with Rias Gremory.