What happens if I open Batreaux chest?
Once the hero has collected a certain number of Gratitude Crystals, a treasure chest will appear in Batreaux's House. Batreaux warns Link that the contents inside the chest are very dangerous. If Link ignores what he says and opens it anyways, he will obtain the Cursed Medal.
If Link goes near it, Batreaux stops him and urges him not to open the chest under any circ*mstances. He states that the chest contains the Cursed Medal, a dreaded medal of the infamous evil according to the Demon.
Batreaux is a demon who lives beneath Skyloft in a shack. You can meet him for the first time during the Lost Child Side Quest. He is a kind demon who has befriended Kukiel. After giving him all 80 Crystals, he becomes human and can be found in the Bazaar during the day, and on the bridge at night.
Once Batreaux turns into a Human, all the enemies at night in Skyloft disappear, excluding Remlits which instead become non-aggressive.
In return for your efforts, he'll give you a number of rewards. You need to collect all 80 Gratitude Crystals to fulfil Batreaux's wish and, once you've accomplished this goal, monsters will stop prowling Skyloft at night and Remlits will no longer attack you.
The Hylian Shield is the best shield in Skyward Sword, because it's larger size provides more protection and it happens to be indestructible.
How to Get all 80 Gratitude Crystals in Skyward Sword HD - YouTube
You can store the Cursed Medal in the Item Check to get rid of its powers. A Pink Fairy in an Empty Bottle will still revive you when you hold the Cursed Medal.
If he tells her that he likes her, she will reward him with five Gratitude Crystals and Fi's comment will change to confirm that Link is interested in Peatrice, and advises him not to mention her around Zelda.
In total, there are eight different rewards on offer, with four of them being upgrades to Link's wallet. Those looking to buy some of the game's more expensive items will therefore need to dedicate some time to finding Gratitude Crystals, though the game can still be completed without doing so.
What happens if you give the letter to Karane?
In the Knight Academy, Cawlin writes the letter to Karane, telling of his crush on her, but cannot bring himself to give it to her in person. As a result, he prevails upon Link - another fellow student, who he has belittled and attempted to bully as a henchman of Groose - to deliver it for him.
Afterwards he leaves finally leaves home and begins to mingle with the people of Skyloft, and starts hanging out at the Bazaar during the day and the bridge at night, due to the monsters having disappeared and Remlits no longer becoming feral, due to the disappearance of Batreaux's demonic aura.
If he tells her that he likes her, she will reward him with five Gratitude Crystals and Fi's comment will change to confirm that Link is interested in Peatrice, and advises him not to mention her around Zelda.
Afterwards he leaves finally leaves home and begins to mingle with the people of Skyloft, and starts hanging out at the Bazaar during the day and the bridge at night, due to the monsters having disappeared and Remlits no longer becoming feral, due to the disappearance of Batreaux's demonic aura.
If all 80 Gratitude Crystals are collected and traded then it will transform Batreaux to his human form which will also rid Skyloft of all monsters.
Give letter to Karane in Zelda: Skyward Sword explained
Give Karane the letter and she'll be more worried about what Pipit will think than Cawlin's feelings. With this in mind, head up the stairs and tell Pipit about Karane receiving a love letter.
