This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 竛 is uncertain. It visually combines 立 and 令, but the original semantic and phonetic roles are unclear.
Since the meaning is uncertain, focus on the shape: 立 (stand) beside 令 (order). Picture someone standing at attention after receiving an order, but remember the meaning is unclear.
For レイ, imagine a person standing (立) and receiving an order (令) from a ray of light: ray -> レイ.