The developers of Honkai: Star Rail have released a video in which they talk about what Cipher is capable of in battle.
Cipher is a quantum type character who follows the Path of Nothingness. She is a demigoddess and the founder of the three hundred noble bandits of Amphoreus, and she herself, the three hundred and first bandit, robs the rich to help the poor.
When using the skill, Cipher deals quantum damage to the selected enemy and nearby targets. Before the skill deals damage, there is a chance that Cipher will apply Powerlessness to the target, this status reduces the damage dealt. And Cipher's attack power will increase for several turns.
When Cipher uses a skill or super ability, her primary target becomes the Frequent Customer. When the Frequent Customer is attacked by allies, Cipher will immediately perform a bonus attack on it.
When using her ultimate, Cipher deals quantum damage to the target enemy and adjacent targets. She then deals true damage equal to the current recorded damage. The higher the recorded damage, the more true damage Cipher deals. This true damage is split between all targets of the ability.
video: https://youtu.be/oSXzdXHyhrI