さ - Casual よ

さ is a casual, masculine-flavored sentence-ending particle used to convey assertion, emphasis, or a laid-back tone. It often marks a statement as casual or informal and can soften the formality of the sentence, especially among friends or in informal settings. When followed by よ, the speaker asserts something with a confident, shared feeling or reassurance, though the pairing with よ is less common than with other endings and often relies on conversational context to feel natural.