There is a small rift in the lower Suthorn Forest and Tri can create an entrance into it.

Find Tri's Friends, Part 1

Go east up the sideways trees. Defeat the two dark monsters, then use echoes to go up onto the treetops. Check on the glowing object to find one of Tri's friends.

Find Tri's Friends, Part 2

Go west down the sideways trees, then go north to a large wall of sideways trees. Defeat the Peahat there, then go up and to the east, where there is a glowing wooden box. Break or burn the boxes with echoes or swordfighter form, then check on the glowing object to save another of Tri's friends.

Find Tri's Friends, Part 3

Go west to the large wall of sideways trees, and use echoes to get on top of it. Then from the east side of the wall, go north and check on the glowing object to rescue another of Tri's friends.

Find Tri's Friends, Part 4

Go to the west side of the large wall of sideways trees, and go south from there to reach a new part of the area. Go west on the sideways tree and upright tree, then go west and defeat the Spear Moblins, the Rope, and the dark Moblin. Check on the glowing object that the dark Moblin drops to save the last of Tri's friends.

There will be a cutscene. Tri's level gauge will increase. You receive 2 Might Crystals.