A power unit for a toy or a system of toys that can removable receive the power unit. The power unit comprises a drive gear that can provide rotational power to one or more driven components of a toy with which the power unit is associated. The drive gear can comprise multiple drive portions. The toys can comprise a wide variety of toy types.

A toy top includes: a body and a shaft part respectively having first and second portions facing each other in an up-down direction in a combined state; and a sliding contact surface which is on the first portion and abuts a projection on the second portion by biasing force of a biasing member. The projection continuously slides from a first position corresponding to a most deeply combined state to a second position corresponding to an uncombined state. The sliding contact surface is an inclined plane which, in the combined state: as a whole, inclines with respect to a plane at right angles to a shaft line of the shaft part; has a level in the up-down direction being continuously lower from the first position toward the second position; and can keep abutting the projection at an arbitrary point.