After a visit to the town doctor--or the closest thing the setting has to a doctor--the pair learns that they now both have the same dangerous affliction. This affliction has apparently tainted both of their souls--something Guts blames himself for despite Tapi's repeated reassurances. The biggest blow to the pair, though, is the doctor's orders to stay out of battle entirely until he can cure them, something Guts undoubtedly will struggle with since battling is his favorite activity.
(Once more, pokemon-shaped pokemon are hard, but that's what practice is for!)