Southwest of Goron City, there is a rift where Tri can create an entrance.

Find Tri's Friends, Part 1

Go east and create a flying monster echo. Pick it up and stand in the air vent and glide over the lava. Then use the northeast air vent to glide northeast, and go from island to island. Use a flying monster echo to glide west to the island down below with the glowing object on it. Check on the glowing object to rescue one of Tri's friends.

Find Tri's Friends, Part 2

Use a flying monster echo to float up in the air vent to the lava area to the west. Defeat the Fire Wizzrobe, then use the air vents to float to the west island, where there is a glowing object. Check on it to rescue another of Tri's friends.

Find Tri's Friends, Part 3

Go back east, then go northeast to the island with a ladder leading down. Go down the ladder. Defeat the dark Moblin on the left and check on the glowing object that it drops. If the glowing object ends up on an air vent, create a rock (not a boulder) to drop on the air vent and block it, then check on the glowing object to rescue another of Tri's friends.

Find Tri's Friends, Part 4

Use a flying monster echo to float up in the air vents and reach the glowing object. Create a rock (not a boulder) to drop on an air vent and block it, then check on the glowing object to rescue another of Tri's friends.

Find Tri's Friends, Part 5

Go down to the bottom of the area and create rocks (not boulders), and you can try to throw them onto the air vents below and/or press X to bind to a rock and drop it on an air vent. Then fall down below, put a rock on any remaining air vents, and check on the last glowing object to rescue the last of Tri's friends.

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