Ossan

He is a veteran solider with Grania Republic, who has a high level of technical expertise, he first lived with Mizuno but has move in with Souhei after he rebuilt his house which was previously destroyed by the girls. Surprisingly, he is also an aspiring doujinshi.

His rank is unknown, but it is suggested that he either has the rank of Master Sargent or Sargent Major.

(Source: ANN)