The Toki Toki no Mi is a Paramecia-type Devil Fruit that allows the user to send themselves and others forward in time. It was eaten by Kozuki Toki, but with her death, the fruit has returned into circulation.
So far, the only strength of the fruit is the user's ability to transport themselves or others out of dangerous situations by moving into the future, as shown when Toki transported her son and retainers to help them escape from the burning Oden Castle.
It is impossible to travel into the past, meaning that all trips forward in time are irreversible. Otherwise, the user is affected by the standard Devil Fruit weaknesses.
During her life, Toki had used this ability to travel further and further into the future, allowing her to live in many different time periods. She used this fruit to enable her son Momonosuke and her retainers to escape from the burning of Oden Castle, sending them 20 years into the future.
At least 830 years ago, Toki ate the fruit and gained the ability to time travel to the future, having used the fruits ability to travel and live from one time period to the next, eventually landing herself 30 years before the present where she finally settled down and married Kozuki Oden.
She last used her ability to send her son and half of the Nine Red Scabbards twenty years in the future before her death, returning the Fruit to circulation.