Katarina's father and Keith's adoptive father. A duke as well as the current head of the Claes family.

Spoiler

After Katarina was engaged to Prince Gerald, Luigi sought out Keith from his relatives who was said to have strong magic powers. He took Keith as his step-son which created problem in their house, almost causing his wife Miri to divorce him. When he further explained Keith's background, everything in their how have calm down and his relationship with his wife got well.