シャイ

しゃい
na-adjective
shy
informaldescriptive
1. shy, timid
Feeling nervous or uncomfortable around others, especially in unfamiliar social situations. A loanword used as a na-adjective.
He has a shy personality.
I'm too shy to start conversations myself.
It is said that many Japanese people are shy.

シャイ is a loanword from English "shy."

Similar words

シャイ is used casually in conversation. In more formal writing, 内気(うちき) or ()ずかしがり() would be more natural.