Transistor is an action RPG set in the futuristic, sci-fi themed city Cloudbank. The player controls the character Red, a famous singer. She is attacked by the robot force Process led by a group called The Camerata, but the attempt fails and they leave behind Transistor, a greatsword-like weapon that has absorbed the man that was last killed with it. During the game Red is hunted down by the group and gets to wield the sword that has its own personality and acts like a companion.
She explores the environment, fighting enemies with a battle system that combines both real-time elements as well as a turn-based planning phase called Turn(). The turn-based approach is only available during battles where a part of the environment is fenced off. During the planning phase different actions can be selected, both movement and attacks, filling up an action bar near the top of the screen. When done they are executed one after the other. It takes some time before the bar is recharged, but meanwhile real-time movement and actions are still possible. Destroyed processes often leave behind cells that need to be picked up or enemies respawn. The areas usually have walls that can be used as cover. Through the battles Red gains experience used to acquire Functions, powers from the Process. These can be equipped as one of four techniques and can also be used to enhance existing techniques.
A large portion of the gameplay is based around experimenting with different configurations of Functions. Skills are divided into active, passive and upgrade slots and most are unlocked by reaching new levels. Any function can be used for each of the three types of slots. The active slot is the main power and it can be enhanced with one or more functions in an upgrade slot. Passive slots are separate and provide passive effects. By switching and combining functions in active and upgrade slots, a specific fighting style can be created. This is encouraged in the game through the inspect command where parts of the story and the characters are revealed by equipping functions in certain configurations. Certain enemies are also more vulnerable to specific types of attacks. There are melee and ranged attacks, with additional effects such as a damage radius, a bounce effect etc. The Jaunt function is used to quickly get out of the way and a 'backstab' position behind an enemy often provides more damage. Through certain functions enemies can be turned to provide help. The screen to customize functions is activated by using a terminal. Optionally limiters can be used to make the opponents of the Process stronger, but with more experience in return.