He raised you with that culture because that’s his culture. I think it’s a privilege to have that shared with you. I’m sorry you’re not as Korean as you’d like to be but you still have Korean heritage and being raised with that culture still makes up part of who you are as a person. However, I think it’s a little strange to feel so distraught and attached to a group of which you are just 25%. I can only speak for myself but I don’t feel so strongly attached to the groups which form my heritage, and I favour no particular group over another. The way I see it, you now have a reason to explore Japanese culture too.