They aren't "suddenly" going to the beastmen country--it's more than likely that the fruit they are talking about is something that can help stabilize Kouichi's current condition. Whatever he drank was probably something he wasn't supposed to drink and the fruit that can only be found in the other country can help neutralize it's effects.
Also, it's more than likely that the beastfolk either; A. go into heat at night. B. turn into actual beasts at night.
Which are both really good reasons as to why they would need to get indoors ASAP. Kouichi still isn't in good condition and Caius--even tho he is a titan and the strongest knight they have--is still only one person. He wouldn't be able to fend off an entire village full of beastfolk if either of those options happened.
They aren't "suddenly" going to the beastmen country--it's more than likely that the fruit they are talking about is something that can help stabilize Kouichi's current condition. Whatever he drank was probably something he wasn't supposed to drink and the fruit that can only be found in the other country can help neutralize it's effects.
Also, it's more than likely that the beastfolk either;
A. go into heat at night.
B. turn into actual beasts at night.
Which are both really good reasons as to why they would need to get indoors ASAP. Kouichi still isn't in good condition and Caius--even tho he is a titan and the strongest knight they have--is still only one person. He wouldn't be able to fend off an entire village full of beastfolk if either of those options happened.