The North Sea has played an important role in European urbanization. Coastal cities thrive on the basis of port economy; but also shrink significantly once the dominated industry recessed. Today, under the threat of climate change, port-dominated homogenous development becomes rather vulnerable to disturbances. Den Helder is the Wadden port-city encountering severest shrinking rate. It is particularly sensitive to environmental change and economic shift, regarding to coexistence of tidal ecosystem protection, maritime activities and rising flood risk. To facilitate reciprocal collaboration between ecosystem and economy, the project explores ‘Nature-Based Solutions’ as an integrated coastal zone management approach for interdisciplinary risk adaptation. In design fiction workshop, a catastrophic 2053 flood is fabricated to facilitate local imaginations on a more nature-based future. Qualitative narratives were structured into a prospective Building-with-Nature scenario, challenging the Business-as-Usual projective scenario. Through backcasting, an adaptive pathway for current shrinking Den Helder is proposed, comprising three strategic phases: utilize, guide and oppose according to risk index. The spatial design employs these strategies in two transformation cores: port-front residential and suburban agricultural polders. By reusing existing canal system to deliver tidal ecosystem services, this backbone synergizes a holistic regeneration that aligns to conserve-release-reorganize natural adaptive cycle. An integrated package is proposed, combining technical renovation of houses, de-polders and a PPP insurance model to incentivize participation and to share the risk. The project is concluded with an open-ended scheme in which shrinking is addressed as part of natural secession. Sequence of actions are suggested based on economic vitality and capacity of ecosystem services.