While the current urban public space pays more attention to the physical construction for the promotion of public health, systematic and specific studies on mental health is insufficient. Through the selection of a specified group of users and the analysis of their mental desire, this article explores the possibility of promoting urban mental health by spatial design. The "Tokyo Loneliness Tree Hole Plan" project suggests reconsidering and reshaping the positive perception of loneliness based on the Salutogenesis Theory and proposes a design guideline for tackling urban loneliness. The project utilizes a scenario-based research method to conceive a systematic strategy for establishing an urban "spiritual infrastructure," which offers the lonely individuals a chance to get along with themselves, the space, and the feeling of loneliness. As the new typology of urban public space with publicity and privacy simultaneously, "Urban Tree Holes" create empathy about solitariness between natural landscape elements and humans in oriental design aesthetics, in order to mitigate the urban loneliness and respond to the mental desire. "One Person Park" as an alternative form of future landscape investigating the concept of "private-public space," which might fulfill the new desire of using public space in a post-pandemic era.