A transformation is a particularly unique concept where a character transforms into a stronger, or weaker (if you're Kanji) form, which is a recurring theme throughout the Goketsuji Ichizoku series, first introduced in Power Instinct. While they are a recurring feature, they are not implemented in all of the games, and in those that don't have them, they usually appear through special moves or win poses.
Initially, Otane Goketsuji was the only playable character capable of a transformation, along with Oume, her sister. However, as the series progressed, more transformable characters would make their debut.
These transformations are usually accessed by means of a throw, but there are exceptions to the rule; For example, a special move can be used to suck energy out of the opponent and transfer it to the other character, such as with Kurara. In either case, the transformation lasts for a limited time (usually 10 seconds), giving the player a short while to use it to their advantage. A couple minor transformations, such as Sahad's or Kintaro's in Power Instinct Legends, could also be interrupted by a single strike. Additionally, these transformations also come with their own movesets and special attacks.
In the case of Kanji Kokuin, however, he stays in the form he transforms into unless a specific move is performed that switches him to and fro. This applies mainly to the first two games he appeared in; In the latest games, he no longer has this feature and his transformation is as normal in that it lasts a limited time like the others.
It's important to note that while a character is transformed, their Stress (or Super) meter cannot fill up for the duration of the change.