The idea for the Ikari gauge (renamed the POW bar in the Western release) was inspired by a Street Fighter II match that background designer Tomoki Fukui had with series creator Yasushi Adachi.

"Adachi came up with the idea, but the inspiration for the Ikari gauge came when the dev team was all playing Street Fighter 2 together for research purposes. Adachi and I were playing against each other and I frustrated him because I won. Adachi was so mad because he lost that he was silent for a minute. Then, he suddenly got up and shouted “Ikari gauge!” So we took that frustration, that anger and rage that players feel when they lose a battle, and decided to incorporate it into the game. That was where the inspiration for the Ikari gauge came from."
Contributed by DrakeVagabond