Finding courage with 気が大きくなる
気が大きくなる means to become uninhibited. They become more courageous than normal.
The expression 気が大き means you don’t care about the small things. You’re uninhibited. Adding なる denotes the action of becoming uninhibited.
Examples
ひとりぼっちの○○生活 » Volume 1 » Page 22
Further Reading
- Garrison, Jeff et al. Kodansha's Dictionary of Basic Japanese Idioms, Kodansha, 2002, p. 233