Omagatoki: Critical grants all allies the effect of having their next individual attacks be guaranteed Critical hits, regardless if they're physical or magical. Resistances do not block Critical hits if they're enhances by Omagatoki: Critical, meaning the attack will resist and land a Critical simultaneously. The Critical hits cannot land a critical on attributes a demon nulls. However, Guarding still blocks Critical hits.
The effect lasts until the end of the faction's turn. The Magatsuhi gauge needs to be full and used up to execute the skill. As it's a Magatsuhi skill, no icons are used, and the turn isn't passed to the next demon.