These are the three blades Ryo will use in CotT, all of them actually being the same item, but it changes along with Ryo himself. These may contain spoilers, so beware.
Old Trusty Sword
This is the sword Ryo starts out with and defeats three Bosses with. It's a nameless blade that looks as if it'd fall apart at any moment due to wear, but it never gives in. It's been re-sharpened numerous times and has been Ryo's traveling partner all his life. It's a broadsword, so it kind of looks a little small for him. But never underestimate its power while in Ryo's hands.
After receiving all three Key Shards from the three tribes - Zoras, Gorons and Kokiri - Ryo's Old Trusty Sword transforms into a beautiful blade called Heaven's Secret. This weapon is a Claymore, a two-handed sword Ryo uses with only one hand, and it's been said it was forged by the Goddesses. Now, why would the Goddesses do that? They don't use blades. Maybe a gift for their son in the first place...? This sword is capable of blocking most magic attacks like a Mirror Shield and when it swings, fire flies in the air from the blade. This is a weapon that evil will learn to fear.
Judgement by Fire
When Ryo transforms into the Fire Deity, so too does his sword change again to Judgement by Fire. The sword is enormous, heavy, sharp, lethal... did I mention heavy? It's a terrifying sword to face, when paired with its partner it can slice stone as if it were paper, torch and slice through all foes and its holy light corrodes evil beings with its touch. When Ryo transfigures back to his mortal self, so too does his sword change back to Heaven's Secret.