Although you've already fought your way through the Yiga Clan Hideout and defeated Vah Nabooris in Legend of Zelda: Breath of the Wild, Queen Riju of the Gerudo is pretty reticent to give up the thunder helm to Link. If you want this swank piece of armor that will grant you the "Lightningproof" ability, you're going to have to show Riju that you're a friend of her people.
The way you prove this is by completing four additional side quests, according to BeardBear's YouTube walkthrough. If you're a little lost on how to proceed, we've got you covered. Here's how to get the thunder helm in Zelda: Breath of the Wild.
Zelda: Breath of the Wild thunder helm guide: "Tools of the Trade" side quest
The first thing you'll want to do is head out of the palace and into the main bazaar, where you should see a woman named Isha deep in thought. Talk to her and she'll explain the problem: now that the Divine Beast is cleansed, she's expecting to get a lot of customers at her jewelry store, but she's run out of flint! This means no jewelry for anybody. She's hoping for a good samaritan to give her 10 flints, but she's not hopeful. Time to put on your hero hat and prove her wrong!
Hopefully you've got enough flint to give to Isha outright so you can mark this quest done, but if not, IGN says you can find flint by breaking open the blackish ores you find in caves and on cliffs. Give her 10 and she'll be in business. She'll even give you a free accessory for your trouble. Nice!
Zelda: Breath of the Wild thunder helm guide: "The Mystery Polluter"
For the next quest, head left from Isha and then turn right up an alley, where you'll see a small, dejected girl standing in some fresh earth. Her name is Dalia, and she'll explain that she put in a lot of the work to try and make an orchard in the city, but some complete jerk keeps throwing garbage in the sluices, making the water unusable for planting anything.
To find the absolute monster who's doing this, head back to the palace and climb up on the righthand side of the walls as you're facing it. You should see someone lounging around on the top portion of one of the water troughs. This is Calyban, and she loves eating melons.
Once you explain the situation to Calyban, she's extremely unrepentant and continues to toss her discarded melon rinds into the irrigation lanes, but says she'll stop throwing her garbage into the city's water if you get her 10 wildberries. The easiest place to find them is in the Rito Stables, so warp there if you're able to. Once you get Calyban the 10 wildberries, she'll not only agree to stop littering, she'll also help Dalia out with her orchard, which will grow wildberries that Dalia will let you pick for free!
Zelda: Breath of the Wild thunder helm guide: "The Search For Barta"
For the next quest, you'll want to talk to Liana in the bottom level of the Palace. By eavesdropping on her conversation with two other guards, you'll learn that Barta (who you rescued from the Yiga clan) went to the southwest in order to check out the Leviathan bones and hasn't come back. She'll ask you to find Barta for her and bring her back home, again.
So the first thing you want to do is pick up a hearty durian in the bazaar. It's only 60 rupees, but you'll need it to finish the quest. Once you've done that, head to Hawa Koth Shrine in the southwest corner of the desert, where you'll see Barta kneeling by the bones of the leviathan. She'll put on a whole song and dance about how this is the end and it's too late for her, but she'll lament the fact that she's dying without eating one last hearty durian.
Once you give it to her, she'll make a "miraculous" "recovery" and then suppose that she'll just hang out for a little while until you tell her that her boss is mad at her. Once she agrees to go back, talk with Liana, who'll give you a silver rupee for your troubles.
Zelda: Breath of the Wild thunder helm guide: "Medicinal Molduga"
The final quest you'll have to complete to prove to Riju that you're a man of the people is "Medicinal Molduga." In the lower level of the palace, you should see a woman named Malena, according to Caticulated. She'll tells you that she just got married to the love of her life but he's very sick. The only thing that will save him is the guts of a Molduga, and she'll ask you to get those guts for her so she can have her happy ending.
You'll find the Molduga at the Southern Oasis, so take a sand seal out there and stock up on some thunder weapons if you can. If you stand up on one of the rock formations near the Southern Oasis, Molduga won't be able to attack you and you'll have free reign to throw bombs in his path, much like you did a certain other enemy type in previous Zelda games. Once the bomb explodes inside him, he'll flop over helplessly where he's vulnerable to your attacks. Use a thunder spear or sword for the best results and just be patient.
Once you've liberated Molduga's guts from his ... uh, guts, head back to Malena, who's so happy that she'll give you a gold rupee for your troubles.
With all four quests done, you can head back to Riju, who said she heard about everything you've done for her people, and will agree to let you borrow (not keep) the thunder helm. It'll give you "lightningproof" protection when you wear it, making it really handy for any area where you're anticipating a lot of thunder-type attacks. Not bad for a hard day's work.
More Zelda: Breath of the Wild tips, tricks and guides
Find out all there is to know about Zelda: Breath of the Wild, including what to expect from the Wii U version, how to preserve your items, how to beat bosses like the Stone Talus, Lynel, the Guardians and the Hinox, the best recipes for Link, how to take on the game's shrines and our coverage of the game's outfits, like the Climbing Set, the two sets of heat resistance armor you can find and how to dress Link in the classic green tunic. You'll also want to find out where all the great fairies in the game, all available stables, how to use amiibo with your version of Zelda and how to increase your health, stamina and weapon slots.