It is important yet challenging to coordinate the motion of a swarm of mobile agents as a cohesive group. In this paper, we focus on the fission problem of splitting the coherent group into multiple sub-groups for the swarm system without identifier and explicit communication. We propose a novel motion control algorithm which integrates a following interaction with the long-range attraction, short-range repulsion, and consensus-based alignment behaviors, where the following strategy is locally applied to one of the proximity neighbors based on the changes of their motion. Through this algorithm, flocks can be split into multiple sub-groups autonomously when multiple agents with distinct preferred directions are introduced. Finally, simulation examples are provided to illustrate the effectiveness of the proposed method in fission maneuvers.