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Since 2009, we have organized a series of scientific sessions entitled"Continental-Oceanic Mutual Interaction: Global-scale Material Circulation through River Runoff" at the Japan Geoscience Union (JpGU) Annual Meeting. The series has explored the dynamic exchange of heat and materials between land and ocean systems, highlighting global-scale interactions such as the correlation between Amazon River discharge and SST anomalies associated with ENSO and the Tropical Atlantic. These studies emphasize the river-ocean continuum as a key regulator of planetary climate stability. In recent years, we have extended this framework through the concept of the Core Biome Complex, which envisions terrestrial ecosystems as adaptable units that could function within extraterrestrial environments. Building on this foundation, the 2026 session expands the discussion beyond Earth to investigate planetary-scale ocean systems and their implications for planetary climate and habitability. The session will focus on: (1) Evaluating the climatic influence of ancient oceans on Mars and their possible role in sustaining transient habitable conditions; (2) Assessing the feasibility and scale of artificial oceans in future terraforming scenarios, from atmospheric engineering to hydrological cycling; and (3) Comparing ocean planets and non-oceanic (dry) planets to clarify how the presence or absence of global oceans affects long-term climate stability and biospheric potential. Through these discussions, we aim to connect Earth-based understanding of river-ocean interactions and material cycles to planetary climate evolution and the design of future habitable environments. We welcome contributions from Earth scientists, planetary scientists, climate modelers, astrobiologists, and others exploring the frontier between natural planetary processes and engineered habitability.