Secondary weapons are an important combat mechanic in Valkyria Revolution. They are limited-use in nature and can be selected from the Battle Pallette, a menu that freezes time and allows the player to choose a course of action. When accessing the Battle Palette, select a secondary weapon that suits the situation.
Secondary weapons include grenades and guns (among other weapon varieties), and will eventually wear out if overused in battle. The exception to this is when you access acquired bases, where secondary weapons can be restored and re-equipped. Grenades and bullets are best saved for particularly overwhelming foes, whereas magic and spellcasting can be used more liberally as a regular part of your combat arsenal.
Mastering the use of secondary weapons is key to your battle strategy, so don’t neglect understanding them. The better you can match your arsenal to enemy weakness or opportunities to attack, the more success you’ll have.