Did you notice something about the OP? During the chorus of the song where they introduce the other characters, we get-
- Everyone from Wei
- Zhang Liao
- Everyone from Shao
- Zhou Yu, Sun Shang Xiang, Sun Quan
- Dong Zhuo and Jia Xiu
- Lu Bu
... And then a mysterious figure in a snowstorm. Looking carefully (with a bigger screen and quality) I could see the person carrying a sword. Now, my main suspects are Gan Ning and Gongsun Zan, because they didn't appear, hell I've even considered Liu Bei- But the problem is that non of them fit the shape of that person.
EDIT: Actually, now that I look closer, I think that's a man's build
no, you just need to have seen the 3 main endings. There's no way you can get them all in one go.
Dong Zhuo and Jia Xu he hid as his personal servants to prevent the coalition from tearing them apart, so to speak. Lu Bu surrendered after being promised food and not to destroy her home.
Yuan Shao and co. never join you, but you beat them up and take over the northern part.
Cao Cao falls under a spell by Gan Ji(one of the two sorcerors) and moves her army against you. Beatings all around and finally her underlings pick up that something is wrong, go to you for help. As gratitude, she surrenders.
For Wu, there's a split in power as Zhou Yu tries to worsen relations and Sun Quan wants to patch up. Finally, Zhou Yu launches a coup. During the process, Sun Shang Xiang decides to try attacking and fails, getting caught, Sun Quan, Gan Ning, and Lu Xun join you in a request to retrieve the Wu lands. Scenario results in Zhou Yu sitting alone in the burning palace.
Cue final battle. The two sorcerors finally decide that it's time to close the book on this "Gaiden" world. (An alternate telling of the true version) The team marches as the Wu and Wei stop the bulk of the enemy army, letting your main group pass. Inside, Kazutou touches the mirror and thinks about everyone.
About the same time, Yuan Shao and her two underlings arrive at what appears to be a deserted island and overload a matching mirror.
Results: everyone but the sorcerors and Hua Xiong are warped. dead people like Gong Sun Zan and Zhou Yu are revived as well.
So...timeline wise, I'd say this would stretch to...roughly the the battle in Jing Province, given how much time passes.
Just for reference, you have around 14 intermissions to spend 2 major character events and 3 minor characters events. And no double ups. Main characters are 12-13 intermissions worth of time. the minor characters are variable(2-9).