This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
龗 combines 霝 (rain) and 龍 (dragon), likely representing a rain-dragon deity. The exact historical development is uncertain.
The top 霝 suggests rain, and the bottom 龍 is a dragon. Picture a dragon summoning rain, though the kanji's exact meaning is uncertain.
For レイ, imagine a dragon in the rain giving a loud roar: the roar sounds like 'ray' (レイ), and the rain-dragon scene ties back to the kanji's shape.