Hisako Koyama (小山 久子 Koyama Hisako?):
Hisako is a secret G-man, and Ryota's older sister. She usually works in a coffee shop. Her father, Masanobu Koyama (小山 正信 Koyama Masanobu?), was a colleague of Masaki until he was killed in action six years ago.

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