Well, this is actually pretty close to how you would directly assault a fortress before gunpowder artillery, though obviously you wouldn't have balloon catgirls, and since you only had archers, you would build a tower to give you an elevated firing platform so you could shoot down at the walls...
Shouldn't Kaiji be coming up with, like, a cover story? Like, "we are freelance computer programmers, we work remotely" or something. Instead of just hoping the old lady goes away?
Honestly, the dude's been doing a good job. The standard practice appears to be to go until the artist's wrist falls off and then abruptly wind things up with an unsatisfying ending. Whereas, this story seems like it will actually finish.