Batou is the favorite superior of the Tachikomas because he regularly showers them with care and affection; in episode 2.15, it also is apparent that he shares a physical resemblance with their chief programmer. He has even dubbed one unit as his "personal" Tachikoma, refusing to operate any other and treating it with organic oil, both habits which culminate in problems. Later in the series, the Tachikomas' AI starts to develop rapidly, which is attributed to a mutation in a protein chip caused by Batou's oil. Also, since Batou treats them as individuals as opposed to interchangeable units, they begin to view themselves as such, which contributes to the development of their AI.