Kiolilo

Like, in that case, why would Riku just hand over the fruit to Sora, give him a means of establishing a romantic connection with Kairi? Why would he even put the idea in Sora's head? It would be massively shooting himself in the foot

(And of course - win or lose, he remarks 'the winner gets to share a paopu with Kairi' was a joke. Basically all of that was just to rile Sora up, because he thinks Sora likes Kairi)

This type of braid is consistently used for almost all paopu-related items. In order: Kairi's wayfinder, Namine's star charm, and Oathkeeper's keychain (all related items) as well as the keychain of Destiny's Embrace.

The only exception seems to be Terra, Aqua, and Ven's wayfinders which are just tied with brown rope. But there's also one notable addition that I came across.

Soul Eater.

No one's immune to adding a design element just because it's cool, sure. But considering the presence of the braided cord in Kairi's wayfinder introduced at the very start of KH1, it's not impossible that this was intended to be complementary. Whereas Kairi is able to be open about her desire not to be separated from Sora and gives him her wayfinder freely, Riku keeps this same want hidden and is unable to express it. Riku's jealousy and suppression is his darkness... and Soul Eater is a manifestation of Riku's darkness into a weapon.

It's even facing the same upwards direction as the wayfinder (and the star charm and Oathkeeper, by extension) whereas Destiny's Embrace and the Combined Keyblade face downwards.

Of course my next thought was "is it on Way to Dawn as well?"

...Kind of. This zig-zag design is certainly evocative of it. Also very subtly evocative of it is Braveheart's handle, which is actually a little closer to the pattern on the handles of the Combined Keyblade.

I might even say Oblivion's handle is also very subtly evocative (KH2's and KH3's respectively)

...But this is veering far deeper into pure speculation territory. Curious that all of Riku's associated keyblades have some element of this design to them. Does it really mean something? You decide!