Kawaguchi Fumiyo (川口文代) is a Witch of the 503rd Joint Fighter Wing, originating from Fuso and attached with the Fuso Imperial Army. She makes hunting large-type Neuroi her forte, to the point of becoming known as "Big-shot Eater" (大物食い, oomonokui). She became a member of the 503rd Joint Fighter Wing at the same time that those military gains were being recognized.
Fumiyo volunteered to the military and was attached to the 11th Fighter Squadron around the time of the Fuso Sea Incident. However, because the conflict was almost over by then, she wasn't able to achieve much military gains. Afterwards, she was transferred to the 204th Fighter Squadron and was promoted to Warrant Officer during drill practice. She was then persuaded by a superior to receive officer training and matriculated into a training academy.
After being appointed a Pilot Officer, she returned to her home unit and participated in many operations on account of a European support mission at the Ural district. Upon sortieing to intercept a large-type Neuroi that performed a night raid, she commenced her attacks in a powerless Ki-43. After finally running out of bullets, she cast aside attacks with a machine gun and closed in upon the enemy, crushing 2 Neuroi with a Fuso sword.
- Fumiyo is based on Yamaguchi Fumikazu (山口文一).