(Volume One is about World War II. If you're not interested, you can start directly from Chapter 70. The setting has been heavily altered.)
Let's be realistic! Life doesn't give you that much time to brood over your feelings. If you love her, go get her. If you like her, force yourself on her. What's the point of confessing? You'll still get rejected. If you can't win her over, drug her. If she turns against you, post nude photos of her. Worst case, you go to jail. If you don't even dare sit in jail, how can you claim to love her? Once you're out, keep forcing yourself on her. Keep at it until she starts questioning her life, until she thinks the meaning of her life is to be forced by you.
Once Gudako has been tamed like this, won't all the Heroic Spirits under her command belong to me?
(A series where the synopsis has nothing to do with the story... probably? At least Gudako is definitely the heroine.)