Keyblade of heart

The Keyblade of People's Hearts, sometimes referred to as Riku's Keyblade, is a Keyblade created by Xehanort's Heartless from the Hearts of the Princesses of Heart, with the exception of Kairi. In addition to being a combat weapon like Sora's Keyblade, this Keyblade has the ability to unlock a person's heart, releasing the Darkness within.

Design
It has a simple design of red and black, akin to the Kingdom Key, with its teeth forming the outline of a heart. It has a rather dark design, despite being created from hearts of pure light. This is probably due to the means by which it was created. Being that it lacks Kairi's heart, this keyblade has never been seen at full power. It lacks a Keychain.

Kingdom Hearts: Birth by Sleep
The Keyblade of People's Hearts is referenced in the Xehanort Reports as the third type of keyblade, which is required to open the door to Kingdom Hearts.

Kingdom Hearts
After Sora retrieves the Keyblade from Riku and manages to defeat him, Riku stumbles around Hollow Bastion, and eventually runs into Ansem, Seeker of Darkness, who convinces Riku to give Ansem his body. At the same time, Maleficent has used the seven captured Princesses to open the Final Keyhole, but without Kairi's heart, it is incomplete. With Ansem in control, Riku summons the Keyblade of People's Hearts, created from the six available hearts of the Princesses, the hearts of the six captured Princesses, and uses them to construct the Keyblade of People's Hearts. Without Kairi's heart, the blade is also incomplete, and could release the stolen hearts if actually used.

Later, after Maleficent loses to Sora and his friends, Riku appears and "helps" her by unlocking her heart, releasing its darkness and transforming her into Dragon Maleficent. Sora and his friends defeat Maleficent again and she is consumed by the darkness within her.

The friends then track Riku down to the Great Hall, where Riku has used the incomplete Keyblade to summon the Keyhole of Hollow Bastion. He reveals that Kairi's lost heart has been within Sora all along, and that it must be released in order to complete the Keyhole. He moves to release Kairi's heart by using the Keyblade on Sora, but Sora parries at the last second, and eventually defeats Riku.

Despite this, Kairi is still catatonic, and Sora is unable to seal the incomplete Keyhole. In order to save Kairi, Sora turns Riku's Keyblade on himself. This releases both Sora and Kairi's hearts from Sora's body, reviving her, but also completes the Keyhole and casts Sora into darkness. Unbeknown to anyone, this act also produces Sora and Kairi's unique Nobodies, Roxas and Naminé. The Keyblade itself dissolves, releasing the Princesses' stolen hearts. Sora fades into a Shadow just as Kairi awakens, and the Heartless rapidly emerging from the Keyhole force Kairi, Donald, and Goofy to flee.

Kingdom Hearts II
In Kingdom Hearts II, the Keyblade appeared when Roxas was dreaming one of Sora's memories.

Notes and References
Keyblade des cœurs