This paper endeavors to explain how and why self-presentation can affect in-game purchase behavior in Fortnite. As one of the most popular battle royale games in the world, Fortnite employs a free-to-play business model but enjoys a high revenue by selling skins and cosmetics. Using an online survey (N=247), Study 1 explores how Fortnite players' play patterns and three theoretical dimensions of self-presentation (identifiability, self-presence, and self-disclosure) are correlated to actual spending behavior. Study 2 is an interview study (N=11) that further investigates impacts of self-presentation on players? in-game purchase behaviors. Results indicate that higher identifiability, less self-disclosure, and playing alone were positively associated with the amount of money that players spent. In addition, self-presentation could affect in-game spending behaviors from five main aspects: a high demand for uniqueness, a desire to establish self-presence, a pursuit for aesthetics, indicating status as a gameplay strategy, and a highlight of community identity. Our findings not only provide new empirical evidence of nuanced self-presentation practices in spending behavior in online survival games but also inform future research on designing effective game mechanisms and engaging gaming experiences.