The beach house is the "cage" because it is isolated. Tourist spots have a transient population—people come and go. This transience is the perfect breeding ground for the trope: the slow, agonizing process of watching a loved one drift toward a rival, often in plain sight.

The story typically revolves around the deterioration of a primary relationship as one partner is drawn toward an outside party through seduction or manipulation. Identification (RJ01262007)

The work uses the as a psychological and physical tool for NTR development:

If "ntr in umi no ie rj01262007" refers to something specific like a game, anime, or a particular community, could you provide more context or details? This would allow for a more tailored guide or discussion.