Shy or bashful; reserved and timid, especially in social situations or with strangers.
彼は内気でクラスではあまり話さない。
He's shy and doesn't speak much in class.
初対面の人と話すとき、どうしても内気になってしまう。
I always get shy when talking with someone I meet for the first time.
内気な子どもを無理に注目させるのは避けたほうがいい。
It's best not to force a shy child into the spotlight.