splendid
璚 centers on brilliance and splendor, often associated with fine jade or gem-like radiance.
璚 combines 王 (jade) with 矞, which likely contributes the sound and possibly a sense of piercing or brilliance. The exact historical development is uncertain.
The left side 王 (jade) suggests a precious stone, and the right side 矞 looks like a complex, radiant shape. Imagine a splendid jade ornament glowing with intricate brilliance.
For ケイ, picture a splendid jade KEI (like the letter K) shining brightly: K -> ケイ, and the gem's splendor makes it unforgettable.