The one where they're unofficial master and bodyguard but no one really takes it seriously due to the modern times,and the master is in love with the bodyguard, but is afraid that telling him will ruin their relationship since he's been ordering him around their entire lives, but the bodyguard is in love with the master and tries to make him dependant on him so that they will never be separated. They eventually get together but for a while they're just pining dumbasses.
Ichinose-kun wa Itsumo Iinari.