This study investigates how China and the Association of Southeast Asian Nations (ASEAN) have used social media platforms to shape their respective narratives and advance their international interests in the Asia-Pacific region, particularly in anticipation of China's response to negotiations for the Code of Conduct for Parties in the South China Sea (COC South China Sea) in July 2023. The study compares China's and ASEAN's use of X (formerly Twitter) to frame their respective diplomatic relations and representations concerning the South China Sea. The findings show that stakeholders from both sides of the China-ASEAN relationship exhibited a degree of caution in leveraging the affordances of social media to frame geopolitical relations and address the South China Sea issue. Moreover, the author found disparities in narrative strategy between China and ASEAN and among ASEAN stakeholders. While Beijing's narratives regarding China-ASEAN relations and the South China Sea issue often pointed out contradictions in or criticized Western geopolitical expansion in the Asia-Pacific region, they generally featured a moderate and amicable tone when engaging with ASEAN. Conversely, certain ASEAN accounts featured narrative strategies that directly criticized China's geopolitical actions in the region. Nonetheless, their overall approach to China-ASEAN relations tended to maintain a positive and friendly stance, albeit with some ambiguity, as they advanced initiatives such as negotiating a code of conduct in the South China Sea.