Teteru is the chief of Rain Dukemon, however unlike Nike's grandmother, he is just a figure head. Teteru is also Livius father-in-law.

Although he is the chief of Rain Dukemon, he does not have any power like his grandmother. Nike's grandmother scolded him when he gave Nike away as a wife to Livius.

(Source: Soredemo Sekai wa Utsukushii Wiki)