When Keigetsu pulls the “I think it might be contagious” (うつる病のような気がします) card to get the maids to back off, it’s framed as a hilarious, desperate lie to escape the “hell training.”

But notice how the maids don’t instantly attribute these symptoms to her baseline chronic illness shows that Keigetsu’s claim is actually highly plausible. It implies that catching a cold or other secondary infections is a regular occurrence the maids are already used to dealing with.

Given her persistent fevers and coughing fits, Reirin’s baseline condition behaves exactly like an immunocompromised, autoimmune disorder. Because her defenses are always down, she is the perfect target for everyday bugs; meaning she likely becomes a walking contagion hazard to her staff on a regular basis.