"Diluter" is a word in ENGLISH

So young and so lethargic! As though he had been born to sit and stare like this. Ever since Kiyoaki had confided in him, Shigekuni, who would have been bright and confident, as befitted such an able young man, had undergone a change. Or rather, the friendship between him and Kiyoaki had undergone a strange reversal. For years, each of them had been extremely careful to intrude in no way on the personal life of the other. But now, just three days before, Kiyoaki had suddenly come to him and, like a newly cured patient transmitting his disease to someone else, had passed on to his friend the virus of introspection. It had taken hold so readily that Honda's disposition now seemed a far better host to it than Kiyoaki's. The first major symptom of the disease was a vague sense of apprehension.