Translation

平然とした / 無頓着な / 軽々しい

Meaning

Blithe often means casually unconcerned about risks, rules, or other people's feelings. It suggests a light attitude where more care is expected. Be careful: it can sound critical, not simply cheerful.

Examples

• 彼は費用の問題を平然と無視した。
  He showed a blithe disregard for the cost.
• 会社は顧客の苦情を無頓着に扱った。
  The company took a blithe attitude toward customer complaints.