jammed in, shellfish, mediate, concern oneself with
介 centers on being positioned between two things: physically jammed in, acting as a mediator, or involving oneself in a situation. The shellfish sense is a separate, less common meaning that does not clearly connect to the core idea of intermediacy.
介 is traditionally explained as a person 人 flanked by two marks representing boundaries or armor, conveying the idea of being between or mediating. The shellfish meaning is likely a borrowing or separate development.
Picture a person 人 standing between two vertical barriers, jammed in and forced to mediate. The two strokes on either side represent the boundaries they are caught between.
For カイ, imagine a mediator trying to calm a heated argument by shouting 'KAI!' like a sharp, interrupting sound. The mediator is jammed between the two sides, and the sound 'KAI' breaks the tension.
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introduction; presentation; referral; showcase (of a product)
nursing; care; caregiving; caring
intervention
trouble; burden; nuisance; bother; worry
to use as an intermediary
agency; intermediation
marine products; seafood; fish and shellfish
mediation; agency; serving as a medium; acting as an intermediary; acting as a go-between
to use as an intermediary; to mediate; to assist
help; assistance; aid
nursing; looking after
meddling; meddlesomeness; nosiness; interference; officiousness
existing (between); interposition; intervention; involvement
a mere ...; only a ...; insignificant
beheading (as the ending to a seppuku)
helper (e.g. for a sick person); assistant
through (e.g. an intermediary, a medium); via; over (e.g. a network); across; by way of; by means of
cottony cushion scale (species of scale insect, Icerya purchasi)
online dating company; online dating service provider
Computer Mediated Communication; CMC