Among the increasing number of houses planned on small plots of land, this is out of the ordinary in shade and size, A 20-minute train ride from downtown Tokyo, 15-minuite walk from the station. It is a long, narrow trapezoid with a lower base of 3.2m as the frontage, height of 29.3m as the depth, and upper base of 0.7m at the very end of the site. Moreover, there is a local ordinance requiring a 0.5-meter set-back of external walls from the adjacent land. Conditions are extremely tough. From the moment I had looked through the site's situation, I have organized a collaboration system consisting of the client, design, structure, construction and maker, then started off planning.During the initial stage of design, it was agreed on: taking advantage of the site characteristic by ensuring a maximum length of the building; providing a space for fun and structural reinforcement to the building by introducing a slope inside; making the best use of underground space; and turning the entire building into a skin. The over-ground section features skin-like external walls with added transparency letting sunlight permeate the entire building. The floor material is expanded metal letting sunlight fall deeper underground, in the attempt to deviate from the floor's of determinacy function.Since the area below ground is beyond the application of the 0.5m rule, major living spaces were buried underground, presenting a need for further permeability. More specifically, the conventional earth retaining work using concrete was simplified into a plain assemblage of 8 mm-thick steel plates with anticorrosive, heat-insulation and waterproof treatments. This method would not only reduces cost but also ensure an extra 0.5 m to the usual working width.I have named this house 'Lucky Drops', the equivalent to Japanese old saying the best for last'. Every effort is being made to materialize this saying---to turn this leftover plot of land into a place of living comfort.