I was giving it a read before, I think the grass is poisoned or has been GE'd to be resistant to yukkuris, and the starving buns are committing suicide in the river because they know they are going to die.
Funny, with an alternate interpretation without the reading, you could see this as a scene of a inmigration wave of wild yu's going to the city, having a scene of a little one NOT wanting to go to the city leaving the forest she knows, which ironically would make her smarter than the rest in that scenario, but again "alternate interpretation", we know what the pic is really about.
"Yueeeeeeeeeeenn!! Reimyu dun wanna die! Dun wanna dieeeeee!" "Little one, die easy! let's take it easy forever togetheeeeeeeeeer!" Reimu hardly drags its koreimu to jump into the river. The child bites the nearby weeds to resist, but it's no match for an adult one's strenght after all. The koreimu is slowly pulled towards the river. The adult Reimu constantly flaps their braids.
(Guys, I'm as lost as you. Maybe it's just part of a bigger story.)
Felix said: (Guys, I'm as lost as you. Maybe it's just part of a bigger story.)
Well Konakona mentions them committing mass suicide due to their food source either being poisonous or has evolved to be more resisted towards their gluttonous diet. We can't be sure about that until someone does a thoroughly look over of the story and come back to us with a summary or translation. Either way you did a good job translating the comment above.