to leap over
迣 centers on the action of leaping over or crossing a boundary in a single bound.
迣 combines the movement radical 辶 with 世, but the exact historical origin is uncertain. It may have originally expressed the idea of passing through or leaping over a generation or world, but this is speculative.
The movement radical 辶 suggests motion, and 世 can be seen as a barrier or boundary. Picture a figure leaping over a fence marked with the character 世.
For セイ, imagine a person saying 'Say!' as they leap over a hurdle: 'Say!' cues セイ while they leap.