Mushi-Shi is a terrific series, and I would love for some of the questlines and talents to take inspiration from it. I love how despite each episode having a similar premise (trouble caused by supernatural creatures most people can't see), each story unfolds very differently. You never know if you will get a happy ending, a tragic ending, a bittersweet ending, or a creepy ending. I would love that range of possibility for questlines in-game. I also love how it has an incredible sense of mystery and wonder while having Ginko take a relatively scientific and ration approach to the situations he faces.
As for disease, SBS's current stance is that disease won't cause death, but will cause stat or skill loss that cannot be removed until the disease is cured.