In this paper, we introduce a design for an electronic toy that is variable in shape and flexibility by using a structural object called "Ninja Track," which is a belt-shaped object that consists of ABS parts hinged both longitudinally and transversely. When lying flat, Ninja Track is adequately flexible. When the user folds Ninja Track at the longitudinal hinges, it loses its flexibility and becomes a rigid stick. We have created two types of electronic toys as applications of this structure. During the toy prototyping process, we discovered five interactional considerations for Ninja Track. Whilst showing toys at public exhibitions over a period of two weeks, we discovered a few problems with Ninja Track, and we have implemented solutions to these problems.