If you want to have something more powerful than the Master Sword, you probably have bought the Giant´s Knife. And if you have, you have noticed that it breaks. To get a Giant´s Knife that doesnt break, do this:

Go to the chicken girl in Kakakiro. Talk to here and she will give you a pocketyegg. Hatch it and use it on Talon, who sleeps in a house in Kakakiro. Then go back with the chicken to the girl. She will now give you Cojiro, a blue rooster. Go to the Lost Woods and find a man who sleeps at a cut-down tree. Use Cojiro at him. Takehis mushroom and hurry to the potion shop with the old lady in Karakiro. Youm have to go through the other potion shop to get to it. The lady makes a medicin that you should leave to the man in the Lost Woods. He has dissaperd, and instead, a Kokiri girl stands there. Give her the medicine and you will get a saw. You should take that saw to a man in Gerudo Valley. If yuo get there, and the bridge is broken, jump over with Epona. hen he gets his saw, he tells that he has a broken Giant´s Knife. he askes you to go to Biggoron and fix it. Go to Biggoron on top of Death Mountain. The latest vulcano-eruption throwed dust in hes eyes, so you have to get him Eye-drops.
Take the reccipe to King Zora. When you get to him, you can see that he is closed up in something. Go to Zora´s Fountain, and swim to the cave in the back. Go through the cave and find the Blue Fire. Catch it in a bottle and use it on King Zora. Show him the reccipe and you will get a Eye Ball frog. Take that frog to the Lakeside laboratory and show  it to the man. He will make eyedrops. Hurry to Biggoron and give them to him. He gives you a check. Wait a couple of days(Sun´s Song), and then go to him again. Show the check and get your Biggoron sword.