Need help with Warriors Orochi 3 Ultimate. New to the series

Got this game when they gave it away on Xbox One, played it a little and couldn't figure out what the hell I'm doing. I'm not familiar with these type of Japanese games, but I found this one to be intriguing nonetheless.

I've looked around on gamefaqs and trueachievements, but their guides don't seem to match up with what I'm doing. For example, gamefaqs guide shows that I should unlock 'Battle of Nagashino - Redux' already, as well as several other redux missions, but nothing I do seems to unlock them and I can't find a straight answer on why that might be. After every mission, I switch out every character to see if there is someone new to talk to. That's opened only a couple missions so far.

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I'd love to find a well written guide so that I can open every mission, find every character, level them all up, and finish 100% without missing anything/anyone.