In Bionicle Rise, g1 vahi is located in the mouth and it can control The time that the wearer recognizes.
(the present)
G2 vahi is located in the eyes. By expanding the awareness of users, wearer can freely see the past, present, and future.
In my headcanon, Okoto is a pocket universe designed by the Great Beings to protect the upper half of the Vahi, making sure only the lower half could be made in the main universe. It was the last failsafe in case the terra-formation of Spherus Magna went wrong beyond repair: when they are put together, the Vahi allows the user to travel back in time and reset the timeline.