|Aliases||A.I. Program No. 40|
|First Appearance||Chapter 26|
Programmed using both C and Assembly, Forty is more powerful than Saati and Toeni combined, however, due to a programming error Forty possesses two personality modes, a proper clean-freak male personality and a mischievous, fun-loving female personality. With each personality initially unaware of the other's existence, Forty's personality instantly switches depending on whether she says "Boy" or "Girl".
Forty-kun, the boy personality, describes himself as a hard-line conservative who is not interested in Hitoshi's sex-based hobbies. An anal-retentive neat-freak, Forty-kun is a self-righteous good boy with a taste for the nicer things in life. All of these traits were Saati's choices, albeit she wanted them in a little sister.
Forty-chan, the girl personality, describes herself as sensual party girl with a taste for the wild side of things, even going so far as to seduce Hitoshi by using a Hyper Program Option to give herself a more mature body. These were Toeni's personality choices, albeit she wanted them in a younger brother.
Saati wanted a "nice little sister", and Toeni wanted a "naughty little brother"; they got a "naughty little sister" and a "nice little brother".
Wishing to have a new younger sibling, Saati and Toeni snuck a look at this new A.I. while it was still in creation. While the sisters agreed on the age that they wanted their sibling to be, 12, they argued about the gender and personality and pressed too many buttons at once. The end result was an A.I. that had two modes: a male personality and a female personality both within a female body.
Due to Akamatsu's love of how Forty (girl)'s personality would "light up the page", many of her personality traits would be passed on to the Love Hina character Kaolla Su during the latter's creation.
- When Forty was trapped in a Dating Simulation and observed Sailor-man retrieving a box of tissues, she assumed it was for blowing her nose instead of masturbating.