Twinrova has appeared in four Legend of Zelda games: Oracle of Ages, Oracle of Seasons, Ocarina of Time, and Majora's Mask. Usually, Twinrova appears as a boss of a temple in the games, but the pair also shows up as a friendly non-player character in Majora's Mask. The two sisters represent each other as opposites. Koume represents fire, while Kotake represents Ice. Because of this, the two become each other's weakness.
Oracle of Ages/Seasons
In Oracle of Ages and Oracle of Seasons, Koume and Kotake are the organizers of a plot to resurrect Ganon. In Oracle of Ages, they use the sorceress Veran to cause much chaos in the world, lighting one of the two flames needed to resurrect Ganon. Since Ages and Seasons are meant to be played as a two different games, linked together with a password, the game that is linked (in this case, The Oracle of Seasons will be the linked game, but the same applies vice versa) has Link fighting Koume, Kotake, and Ganon at the end of the game. In Oracle of Seasons, Koume and Kotake use an evil general named Onox to fight for them.
Ocarina of Time
Koume and Kotake appear as the boss of the Spirit Temple in this game. Their first scene occurs when Link is a child, just as he recovers the Silver Gauntlets. As Link recovers them, Koume and Kotake kidnap Nabooru, the Spirit Sage, and keep her captive for seven years. When Link returns as an adult, he is able to explore the Spirit Temple and uncover the Mirror Shield, the key to victory versus Twinrova. Before Link reaches Twinrova, however, he discovers a possessed Nabooru, dressed up as a Iron Knuckle. Link must defeat her to release her from her armor and her trance. After this, Link gets to take on Twinrova for real.
Each sister only has one attack, a beam of energy. Koume uses a Fire beam, and Kotake uses an Ice beam. A direct hit will cause 2 hearts of damage, but the beam will also leave a large circle of effect on the platform. Touching this can cause up to 3 hearts of damage, so be careful. Using the Mirror Shield, reflect the beams at the opposite sister. For example, when Koume shoots her Fire beam at you, reflect it back at Kotake. One may find it easier to stand on one of the four smaller platforms on the edge, so that most of the arena is in your view. Z-targeting here can actually be harmful, so instead manually aim your shield at the opposite sister and hit her with the beam.Do this four times total, and Koume and Kotake will join up to create a single enemy.
Now that Twinrova has become a single enemy, she becomes much easier to deal with. The same basic strategy applies here: you must use Twinrova's magic against her. The difference is that you must absorb the magic into your Mirror Shield and then attack. In this form, Twinrova will alternate which beam she uses every three times. To use the magic against her, you must absorb the same attack three times straight. If you happen to interrupt the sequence, you will have to start over. If she uses a different attack, just jump out of the way. After you absorb three straight attacks of the same variety, your shield will unleash the power it has been storing. Once Twinrova is stunned, jump across and slash her with your sword.
Kotake and Koume are friendly characters in the parallel world of Termina. They both reside in the Southern Swamp. Kotake owns and runs a potion shop, while Koume runs the boat cruise. You first meet Koume lost in the Woods of Mystery, fallen ill. If you find Kotake, she will give you a bottle filled with Red Potion. If you give it to Koume, she will be revived and able to resume giving tours on her boat cruise.
Since you helped her, Koume will let you ride the boat for free. This allows you to progress to the next stage of the game.