Please check Images 1 and 2 of the link supplied by Cinefil-san, and click the interactive steps 1, 2 3, etc... of Image 2 to get the whole idea of this process.

The 'Sword' construction method consists in assembling, on a convenient side platform and one after the other on a continuous repeat pattern, large modular sections of the same intended construction level. Once the large assembly has been rear-extended with one more of its modules, it is pushed/dragged by steps toward final position on a multi-slide rail track (=ステップバー, in red on Image 1), to make room for the next module assembly.
the name of this method suggests the parallel pull of a sword out of its sheath.

This contrasts with the earlier method of constructing the whole construction at a much slower speed on the discrete spots of each of its component parts-- which meant multiple changes in the way of bringing the materials where required. This more recent method requires only 1 single spot for material supply and assembly.