What binds us and our partner?
Well, nothing specific, actually. It's just that there's some invisible bond between you two that you must strenghen each time. When your bond is strong enough, both of you could telepathy, or your partner will getting stronger each time.
What is a pact?
A pact is a time when you make that "pact" with your partner. When agreement happens between you both, a certain light will appears surrounding you for a while.
So we're talking about pact. Then we don't get our partner in the beginning?
Not yet. After you enter the world on the other side, you can have your partner.
Anyway, because apparently have time limit during Zero Hour, of course we wouldn't stay for that long in the world at the other side, right? What happens to our partner when we leave them?
They will stay there another day, but each time you enter the world at the other side, you can summon them anytime.
Is there anyway we can leave or change our partner?
Well, you can, but it must be two sides agreement. If you decided to leave your partner, he/she/it must be agree. You can leave or change it if they're die, though.
So after they die, we can get a new partner?
You better do. Surviving the Zero Hour without the help of your partner will be really hard, especially if you're alone or without the help of any other survivor.
Oh yeah, what form does our partner happen to have?
Yeaaa, I nearly forgot about this. As I said earlier, your partner must be original, so I'll appreciate if you're not using existed mythical character or heroes such as Alexander the Great, Goddess Artemis, God Apollo, Odin, Amaterasu, Leviathan, Quetzacoatl, Hydra or anything.
Since I'd like you to come with original idea about your partner, you are allowed to use existing mythical race such as vampires, elf, fairies, gnomes or even create one by yourself. You can also have normal human or animal. Yes, you are allowed to have an animal as your partner.
What ability does our partner will have?
I would suggest anything that's related with their race or their nature. For example, if elfs, maybe their long span of age or perfect archery ability (if based on Tolkien's view of Elves). If fairies, it has wings and it can fly around. Maybe if it's animal, then all of the animal traits would apply to it, such as strong legs and the speed of cheetah, or the hard skin and immense power of elephant (I wouldn't suggest such big animal though). If it's human, you could give traits of warrior, or maybe magician from the other world.
Just remember that nothing is perfect. I would very very appreciate if you give your partner some kind of weakness, which means that there will be room for development for both your human character and your partner.
What is the limit of our partner's ability?
I wouldn't suggest for you to give so many abilities at the first time you meet them. This is due to each partner that is trapped behind the wall, would be just mere spirits, so by having a pact with them you actually give them an actual body. But most of their abilities have lost during their wander in the mirror city. As the story progresses, and your bond with your partner strengthen, you can add some abilities to your partner. Just keep in mind to make their abilities matched with the nature of your partner.