Which version of RPG Maker are you using? You can use states to adjust elemental weaknesses, and in MZ, you can use states to alter the Normal Attack element. You can also have all your skills use the Normal Attack element as well. If you do this, it would be best to only use this method to determine vulnerabilities, as adding in other elements tied to specific skills could complicate things. So, you could have a Sad state with a Trait Effect of Happy Damage 50% and Angry Damage 200%, plus an effect for Attack Element: Sad. Happy, Sad, and Angry would be listed in the Elements section of the Database.