GitHub Sponsors, launched in 2019, enables donations to individual open source software (OSS) developers. Financial support for OSS maintainers and developers is a major issue in terms of sustaining OSS projects, and the ability to donate to individuals is expected to support the sustainability of developers, projects, and community. In this work, we conducted a mixed-methods study of GitHub Sponsors, including quantitative and qualitative analyses, to understand the characteristics of developers who are likely to receive donations and what developers think about donations to individuals. We found that: (1) sponsored developers are more active than non-sponsored developers, (2) the possibility to receive donations is related to whether there is someone in their community who is donating, and (3) developers are sponsoring as a new way to contribute to OSS. Our findings are the first step towards data-informed guidance for using GitHub Sponsors, opening up avenues for future work on this new way of financially sustaining the OSS community.