After you go through the Eldin Volcano, you battle the fire dragon, Volvagia.

How to Defeat Volvagia

First Phase

Volvagia will make a large green fireball float slowly toward you. Afterward, Volvagia spits three fireballs at you. Dodge the fireballs, then bind to the green orb on Volvagia's neck and pull it off. Then collect the energy that falls, and switch to swordfighter form to hit Volvagia repeatedly.

After that, Volvagia will fly to another location. Repeat the strategy until Volvagia roars after popping up from a new location.

Second Phase

Now whenever Volvagia pops up, it may spit two green fireballs, one after the other. It may point its head up and charge up a flame, then breathe fire onto your current platform, making it unsafe, so be sure to jump away as soon as Volvagia starts heating up the current platform. Volvagia will sometimes spit five fireballs.

Whenever Volvagia pauses its attacks try binding and pulling the green orb, then hitting Volvagia repeatedly when it's stunned.

After the Battle

Afterward, there will be a cutscene. Tri's level gauge will increase. You will receive 5 might crystals. There will be an additional cutscene after this, and you will receive Din's Sanction.

Take the Heart Container (or leave it there for an extra challenge), then go to the glowing spot on the left and talk to Tri, and say Yes if you're ready to exit the dungeon. There will be a cutscene. This completes the quest "The Rift on Eldin Volcano".

If you have received the Sanctions from the the other two goddesses, there will be a cutscene that begins the next quest, The Prime Energy and...

Now you can get fireworks in Goron City. Go into Goron City and go up a ramp to the upper level, then go into the northeast door. Talk to Basa to start the quest The Fireworks Artist.