While exploring the school in Brical de Mar in Temtem, you may have come across the Missing Kids quest. Two of the students, Yusuf and Roger, haven’t been seen in a couple of days, and the headmistress wants you to find out where they are.
You are not told this in the game, but you will need a surfboard to be able to find them. Getting a surfboard is a complicated process. First, you need to travel to Arissola and find Sophia’s Dojo there. Sophia is a character you meet in Brical de Mar; she is a friend of the Professor. When you arrive at the Dojo, you will be told that Sophia is not there.
To find Sophia, you will need to travel to the Windward Fort, past the Gifted Bridges, where you will find Sophia trapped in a cell. When you see her, continue towards the fort, then head to the top where you will battle Lady Lottie. Beating her will get you the Windward Key, which will then open Sophia’s cell.
Now, you can return to Arissola and fight Sophia at her Dojo. Beating her will finally get you the Surfboard, and you can now complete the missions and tasks that require it. If you return to Brical de Mar and head to the west of the town, you will now be able to cross the water and will find the two students on the far side. You can see the location marked by the question mark on the western bank.
After that, return to the headmistress and tell her what the boys were doing and receive a reward.