Like many Temtem, Tuwai can evolve, but how they do it works a little bit differently. While most Temtem evolve just from hitting a certain number of level-ups, Tuwai has a unique evolution that is hidden behind a side quest. Tuwai can evolve into Tuvine and become a Crystal-type.
To get this evolution to occur, you must bring Tuwai to the Crystal Shrine, which can only be accessed by completing the Cultist Hunt side quest. To begin the quest, you must first beat Valentina and Federico in a battle. You can find these NPCs in Kupeleleza.
Valentina will use a level 38 Azuroc, while Federico will use a level 41 Volarend. You will discover Kupeleleza on Route 12 on the island of Tucma.
When you beat them in battle, they will ask for help finding the Crystal Cultists. Agree to help them, then check your map for a new waypoint that will have appeared there. Go to this location, and you will be able to start fighting the cultists.
They will refuse to fight you unless your squad is made up entirely of Crystal-type Temtem, so make sure you have lots of different Crystal-types before you go to take them on. There are four fights in total, and when you finish them, you will get access to the Crystal Shrine. This will allow you to evolve Tuwai into Tuvine. When that is done, return to Valentia and Federico and tell them about what you found to receive a Sweatband. This piece of gear will return 15 percent Stamina to any Temtem using it at the start of their turn.
All the cultists will use Temtem between level 30 and level 45, so be sure you have some Crystal-types at the right level so you can win each battle.