Many times I've seen Kasumi's houskeeping depicted as an elaborated kata in her school of domestic arts. It seems reasonable. Housekeepers get more efficient as they gain experience.
Why shouldn't much the same be true for construction workers? Just about every line of work has some equivalent of an Ancient Master who can do things faster and more effectively than others. Nerima has a unique kind of damage going on, and the place is a Mecca for those in the martial arts. You take an Ancient Master and a localized situation, you get a dojo and students - a dojo training workers to both repair damage from the martial arts, and make the repairs strong enough to survive when the next martial artist comes by.
It could be called Martial Arts Reconstruction just as easily, but they make new buildings in Nerima too. Consider these people as similar to the architects and builders that work in earthquake territory.