Alright, it's time - help me figure this bit out. Mitsuami's an abacus - she has the five beads below the rod in her hair, probably a suanpan given the vaguely kung fu outfit she wears. Soroban is a soroban, she's a speccy dork. They fight on the tenth floor - and what seals the battle is something that breaks for Soroban - one of the key differences between a suanpan and a soroban is you can only represent a decimal number with one bead configuration on a soroban whereas the suanpan lets you mess with the extra beads.

But why 10? What's the deal with the counters in the first shot we see Mitsuami? Is this too high a level of a Japanese joke for me to understand? Why can't I have Soroban spit in my face?