you, lord, secretary, state minister
卿 centers on a person of high rank or formal address: a lord, state minister, or secretary, and by extension a respectful 'you' used for such figures.
卿 is thought to combine 卯 (a kneeling person) and 皀 (a food vessel), suggesting a person serving food, which came to mean a high-ranking official or minister. The exact historical development is uncertain.
The outer 卯 looks like a kneeling figure, and the inner 皀 resembles a food container. Picture a kneeling servant offering food to a lord, representing the high status of a minister or secretary.
For ケイ, imagine a lord named Kay who is always addressed respectfully: Kay -> ケイ, and you say 'you, Lord Kay'.
Lord; Sir
cardinal (Catholic Church)
high-ranking court noble; senior court official; kugyō
three secondary Tokugawa branch families (Tayasu, Shimizu, and Hitotsubashi)
nine ministers (of the ancient Chinese government)
six ministers (of the six Zhou dynasty Chinese ministries)
you
court nobles and state ministers
you (plural)
three secondary Tokugawa branch families (Tayasu, Shimizu, and Hitotsubashi)
high-ranking court noble; senior court official; kugyō
court nobles and other courtiers allowed into the Imperial Palace