Wooden Sword

The Wooden Sword is a weapon in Kingdom Hearts. It is wielded by Sora and Riku at Destiny Islands, and again by Sora at Hollow Bastion, when Riku takes the Keyblade. It is also seen in Kingdom Hearts Birth by Sleep as Ventus's practice weapon before Terra gives him the Wooden Keyblade.

Kingdom Hearts Birth by Sleep
The weapon reappeared in the prequel Kingdom Hearts Birth by Sleep, in the possession of Ventus as his practice weapon. At this point, the blade of the sword has many nicks and dents in it from practice fighting. Noticing the damage, Terra bestows Ven with his Wooden Keyblade as a replacement.

Kingdom Hearts
On Destiny Islands, Sora, Riku, and Tidus would often use these toy swords to spar against each other. They would pass the time on their tiny island with friendly matches against each other - Sora and Riku even having a friendly rivalry, the latter usually coming out the victor.

During the destruction of the islands, Sora attempted to stave off the Heartless with the toy sword while making his way to Riku and Kairi, having barely any effect on the Shadows. When he and Riku were covered in darkness, the sword became the Keyblade, which Sora then used until he arrived in Hollow Bastion.

It appears, however, that Riku kept his and it washed up with him in Hollow Bastion. While Maleficent gave him the Soul Eater, he kept the wooden blade around. When Sora arrived in Hollow Bastion, he and Riku had a short standoff, and Riku's strong heart prevailed. Now wielding the Kingdom Key himself, Riku tossed Sora his old toy sword, telling him to go and play.

With the help of the Beast, Sora made his way into the Entrance Hall of Hollow Bastion, where he and Riku had another showdown, and this time, Sora's heart held out. The Kingdom Key chose Sora once more, and the two fought. It is unknown what happened to the Toy Sword after this.

Design
The Wooden Sword is easily the weakest weapon in the game, and possibly the weakest in the entire series (its only rival being Kingdom Hearts II's Struggle Bats as well as the Keyblade Sweet Memories and Kingdom Hearts 358/2 Days's Wooden Stick).

As its name suggests, it is indeed a toy, crudely made from pieces of wood to look like a real sword by the boys of Destiny Islands. It has next to no effect on even the weakest of Heartless, although Sora can still cast magic through it if he knows any. Despite his swordsmanship and magical training, Sora is nearly helpless when using this sword instead of the Keyblade, and must rely on his party members to destroy his enemies, or else run.