No need for a plugin at all, this is easily done with damage coding in default makers.
Please search the forum in the section of your maker (whichever you use, any up from RMXP supports this) for a topic about how to use the damage formula or how to use damage coding or so.
The topic might have a different name depending on the maker, but it should always be one of the pinned topics.
that will list the commands you can add to the damage formula of any skill to give it additional effects beyond "damage to target". That has been used for suicidal skills for decades.