Yukkuri's nature is that the paste in their body turns sweet when they feel suffering.
Reimu, who's feet were torn and whose face was ruined, became very sweet.
When yukkuri's taste-bud are ruined, they can't eat the food they used to eat anymore.
Marisa who keeps on licking the sweet paste will surely ruin her taste-buds.
Reimu can't move anymore, but Marisa will keep on licking on her.