The 'original' Teke-Teke is from a Japanese creepypasta story about a schoolgirl who became a vengeful spirit after having the bottom half her body sliced off by a train (right at the middle of the torso). Variants as to how that happened include getting tied to the tracks by school bullies, or being pushed, or just a simple accidental fall. Anyway, without her legs, the Teke-Teke can 'only' move by dragging herself along with her upper arms, causing a distinctive "teke-teke" scratching noise from which she gets her name. (Some variants have her 'walk' by using her arms as legs, like Ishiyumi's version above, but she still makes that scratching noise).
The Teke-Teke's modus operandi is to ambush isolated victims at night to slice them in half across the torso (emulating her death). This is often done with a Grim Reaper-style scythe. She is also often depicted with an exposed lower spine jutting out at where her torso was cut in half.
Ishiyumi's version above has a missing lower body like the original. Beyond that, her lower spine seem to have been modified and extended into a scythe-like tail, and her upper arms (and hands) have been elongated and reinforced to act as legs.
