Piko Piko one the names Yukkuri Reimu uses to denote its fluffy braids (aside from "Fluffy Fluffy", that's a rough translation of it, and "Mister Braid", accepted by other Yukkuri).
In the original Yukkuri Reimu fanarts, Yukkureimu had only long, hime-cut braids, resembling the ones worn by the "original" Hakurei Reimu, with no special abilities whatsoever. In time, as a stylistic cipher (in-universe explaining by a fast-acting evolutionary drive of the whole species), some Yukkureimus started to show more fluffy, bushy braids (also named "Wasa Wasa"), and all of them gained the ability to move their braids.
The range of movements a "Mister Fluffy Fluffy" can reach ranges from the simple wagging of a dog tail to some degrees of manipulation, much like a tentacle or a crude limb used to grab items or pet koyukkuris.
Other braided species, despite having longer and more ornate lock have started to exibit the same properties of the "Piko Piko": Yukkuri Marisa are known to be highly dexterous with their braids. It's inferred that they simply believed they could outdo Yukkureimus, and they did.