Digital Diplomacy in Motion: How Chinese and Japanese State Media Reframe National Culture on TikTok and YouTube

In the era of algorithmic communication, digital diplomacy increasingly operates through entertainment-oriented platforms such as TikTok and YouTube, where national narratives are shaped through algorithms, aesthetics, and audience engagement. While prior research has focused on textual diplomacy on platforms like Twitter and Facebook, it has insufficiently examined how short-video formats transform cultural representation and state communication. To address this gap, this study introduces the Algorithmic-Cultural Mediation (ACM) framework, which integrates digital diplomacy theory, cultural narrative analysis, and platform algorithm studies. Employing a comparative multimodal discourse analysis of 400 high-engagement videos from CGTN and NHK World spanning 2023 to 2025, the study investigates how China and Japan reconstruct national culture through algorithmically mediated visibility, localized storytelling, and visual design. The findings identify two complementary models of digital diplomacy: CGTN's velocity-oriented strategy, which emphasizes trend adaptation and collective identity, and NHK World's authenticity-oriented strategy, which prioritizes aesthetic minimalism and individual creativity. Both approaches demonstrate that algorithms not only amplify but also reshape diplomatic narratives into participatory, data-driven cultural performances. The study contributes to theoretical understanding by framing digital diplomacy as a process of algorithmic-cultural negotiation and offers practical insights for designing cross-cultural communication strategies within the global platform ecosystem.