信じようと信じまいと

whether you believe it or not

→ 信じる
phrase Rare #38,440
whether you believe it or not An emphatic expression meaning that something remains true or unchanged regardless of whether someone believes it. The pattern can also be used with other verbs to mean “whether you do something or not.”
JA: 信じようと信じまいと、これは本当の話だ。
EN: Whether you believe it or not, this is a true story.

君がそれを信じようと信じまいと僕にはたいした違いはない

Whether you believe it or not makes little difference to me.

信じようと信じまいとそれは真実だ

Whether you believe it or not, it's true.

君がそれを信じようと信じまいと僕にはどうでも良い

I don't care whether you believe it or not.