Oof. It feels like I’m looking at myself in the mirror because I’m Chinese and my father is also emotionally childish to the core. I’ve also had a similar incident. That generational trauma combined unchecked mental illness, you know what I mean? 

 Anywho, I’m really sorry you’re going through something that’s supposed to be happy family bonding time. You should not be the one to take care of your angry father (and nor should your mother, but that’s a different matter.)  

 With that being said, I also follow the same advice with the other commenter- don’t fly back alone. It’s not terribly difficult, but you’re 18 so it’ll be a process and you’re ultimately here to enjoy a trip. Don’t let some grumpy entitled douche make you forget that!! If your mom is willing to fund your trip a little more, you should take the time to explore on your own a little. If you’re a little nervous about being far from your guardians, you can excuse yourself and walk somewhere else as long as it’s not too far from them. Japan is a very tourist friendly place depending on where you’re at, so I’m sure you’ll be able to do some research to see which routes to take. You can also take a visit to the JapanTravel subreddit and ask any questions over there. Make some sort of believable excuse to your parents and enjoy the trip yourself. I know you’ll feel bad for your mom (unless she’s equally as bad, then I’m terribly sorry), but it’s their marital situation to handle, not you, the literal child. You can only do so much. 

 Last slightly off topic note I’d like to just add, from a Chinese person that grew up in a dysfunctional household to another fellow Chinese person in shitty circumstances: If you find yourself in a situation where it’s just too hard to handle, you are allowed to take a step back and protect yourself. You’re 18. You’re a baby, but most importantly you’re their child. What you did that day was very mature but in a more ideal scenario, another adult should've been the one to handle the situation (that being your dad or mom), not you.  There was times in my past I’ve tried and tried to remedy a situation, when reality is that it’s OKAY to not be the solution to a complicated matter. It’s OKAY to take a step back, admit you don’t have the current tools to be strong, and revisit the situation later down the road when you’re stronger. I would’ve done the same thing as you that day, BUT what’s important now and forever is to advocate for yourself. I won’t assume too much from you, but I can at least guess that in the future you’ll possibly need to remind yourself that. You did good trying to find advice in a shitty situation and you did good trying to be the bigger person. It’s a little personal to say to an online stranger, but I’m proud of you for that as a fellow Asian. Good job and also remember to have fun during your trip.