Aki (亜季 Aki) is Haruna's younger sister and a tsundere (a character who flips between a "cold" side and a "warm" side). She initially didn't believe that Hakone was a hot spring spirit.
- Aki sounds like the Japanese word for "autumn" (秋 aki). Aki's name also contains the character for "season" (the time period).
- ↑ http://www.hakone-chan.jp/character.html (Japanese)
- ↑ Hakone-chan ep 2