Japanese by Example
Learning through examples in manga

Becoming uninhibited with 気が大きくなる

Idiom Explanation: Finding courage with 気が大きくなる

ひとりぼっちの○○生活 » Volume 1 » Page 22

Bocchi was up late reading a book on how to make friends. At the time, she was overly enthusiastic, but at school the next morning she finds her social anxiety has returned.

ぼっち:
「夜(よる)は気(き)が大(おお)きくなる」
"Last night I became uninhibited."