Here's how Tokitowa heroine Toki transforms into her alterego, Towa. Toki is the redhead. Towa is the blonde.
According to Famitsu.com's report, the transformation occurs in battle when you build up experience and level-up. Toki will change to Towa, or vice versa.
In addition to having different personalities, Toki and Towa have different battle styles. With her rifle, Toki is good for long distance attacks. Towa is better for close range attacks. Famitsu.com's report suggests that you transform when you're having trouble in battle.
Towa will make her first appearance early on in the game, it seems. As previously detailed, the game begins with the main character -- you -- about to marry Toki. Bandits attack, and your character suffers grave wounds. In this moment of danger, the Towa personality awakens within Toki and does away with the bandits on her own.