What if he failed in his revenge and, upon his defeat to Kihara Byouri, control of his physical body was taken in some way? What if he was ordered to attack one of the people he most wanted to avoid baring his fangs against?
To escape such a situation…
“There’s something embedded in here,” muttered Kumokawa Maria. “That freed him from being controlled like a doll!!”
It was nothing more than a small semiconductor.
A list of how Kihara Kagun would act given certain conditions had been inserted as a string of 1s and 0s. Kihara Kagun was not thinking using the brain of Kihara Kagun.
However, a tiny effect would appear only when he was forced to do something that was “not like him”.
He wanted to ensure that he would take the actions that were “like him” based on the list he had inputted into the device.

Toaru Majutsu no Index New Testament vol.8 ch.4 pt.18