Forced Termination

Forced Termination (強制終了) is unique amongst the other phenomenons in the sense that it is not initiated by the Heartseeds, but automatically activates under certain conditions. This phenomenon appears during the Nise Random and  Asu Random I arcs.

Description
Forced Termination automatically activates in response to two or more people experiencing a paradox as a result of a phenomenon, for example, if two or more people observe the same Illusion Projection at the same time. The ensuing paradox will cause the observers to have their memories reset to before ever encountering Heartseed. Another trigger for this phenomenon is if there is a risk in deteriorating mental state or injury, especially when there is physical violence acted among the members with the same phenomenon. Violent events occured with the StuCS in a few situations but never among the group (eg. Michi Random where the thugs kidnapped Inaba and the StuCS resorted to violence but Forced Termination never happened because it was not used on another member within the group.) It is later discovered that the underlying reason for Forced Termination to activate during acts of violence is due to the members of the group breaking their bonds with each other. To prove this theory to the others, Iori struck Taichi, but neither were terminated because their bond was still intact. When this phenomenon activated in the "Isolation Dimension", the members involved would disappear from the world, which many mistook as returning home.

Heartseed apparently has some control over this phenomenon and was able to return the memories of Taichi and Yui, but not Oosawa. Interestingly, even while his memories were erased, Taichi still had a desire to go to the StuCS clubroom, but did not know the reason. This shows that the memories are not completely erased and parts of it still remains.

Trivia

 * This is the only automatic phenomenon that Heartseed never directly initiates.