Laplace allows Rein to know the precise location and momentum of objects around her and is able to calculate how they'll move based on said information, essentially allowing her to see into the future. Aside from her usual calculations, she is shown to be able to use Laplace on herself, allowing her to enter a deep state of thought which is portrayed as being underwater. However, her sigil can be countered by moving faster than she can see, by teleporting, or by attacks that can affect a wide area.
Using Laplace allows her to gain all types of information about her targets, such as height, weight, estimated age, muscle mass, and athletic ability. She can also use it on drinks to see whether external substances, such as poisons, were mixed in. Using her sigil at full power increases the information that comes in through her five senses, allowing her to see the movements of large numbers of people, including their conversations, expressions, and heartbeats.
According to Rein, using Laplace feels like she's diving in a deep and peaceful sea, and the world around her is likened to a sea of information. Diving deep enough into her sigil can cause her to not notice things happening around her, such as not noticing at first that Kaname was tapping her shoulder and trying to tell her something.
- Rein's sigil name and concept comes from Laplace's demon.
- The kanji for Rein's Laplace translate to "world function" and her sigil uses calculations, differentiating it from Witch's Laplace which translates to "destiny observation" and seemingly sees into the future.