After asking a question, Confession allows the user to force the victim to answer truthfully.
With this Quirk, the user can learn the true thoughts, secrets, intentions, and feelings of allies and enemies alike, allowing for information gathering, psychological torture, and prevention of betrayal. The usefulness of this power has apparently made Overhaul value Shin the most out of all the members of the Eight Bullets.
It's worth noting, however, that this Quirk doesn't guarantee the prevention of betrayal, as people with unpredictable or unstable natures (such as Himiko Toga and Jin Bubaigawara) can simply decide to change their minds on a whim.
Confession has little offensive capability, so the user has to rely on other methods to fight directly.
Shin uses this Quirk to learn of information that Overhaul wanted to know, as well as checking to make sure that no one had any intention of betraying the Hassaikai.
In battle, he plays on people's emotions by forcing them to admit things that they are not proud of.
- Confession - Wikipedia article about the effect of Shin's Quirk.