まい

まい expresses a strong personal intention not to do something, or a prediction that something will not happen. It is somewhat formal and masculine in nuance, and is common in written Japanese or more careful speech. It can convey a firm decision (I will not do X) or a strong supposition (I doubt X will happen). In casual speech, people often use ないだろう/でしょう instead, but まい has a firmer, self-directed tone. When used for probable negation, it often appears with events that are predictable or uncertain from the speaker’s perspective, similar to 'probably not' in English.