I'm going to let you guys fight it out in whatever shape and form you need to become nice and level headed people again. Because if you don't you are all going to get brutally murdered. But on that regard I shall leave you with the words that hundreds before me and hundreds after me will say. Never split up the party you are just asking for trouble. Especially if your GM is feeling a bit sadistic and well Windel likes rape monsters what does that say about Windel in the sadistic category? XD But that is just my humble opinion on that matter.
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Oh and Savo if you want my vote on what to do I would suggest trying to do whatever you can to get up as close as you can against the thing, practically humping against it. Because it has been established it is pretty darn big and is very smart. So facing it head on would just end very badly. Crushing it's windpipe assuming its size would take maybe double that of a human so like 20-30 pounds of pressure. Which you could be able to apply with the rope but it depends if you can get a good enough hold on it, while breaking the violin stick thing would probably piss it off and be able to save the hatter if it doesn't drag the hatter along right with it. And if it is like a real violin stick it might be sharp enough to sever the veins choking her. So really in your current standing without any help from anyone else you are in a screwed if you do and screwed if you don't but so is Mairu.
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Oh and a collab may be smart for you guys yes.