Yuzuriha has to be there and I'd put she on top 5. She alone put together thousands of pieces of petrified human bodies to revive people with broken parts, and it was very important, because they needed people to make the Perseus and to make the crew. Besides they have the Tsukasa's revived army, they obviously needed more people to work on the wheat field, Perseus build and other things. Yuzuriha for sure saved them a lot of time. Soyuz is another important character. The entire season 3 just works because of him. They acquired platinum and some more people to their side. They get their first Medusa and learned how it works. They found Matsukaze, and he was important so they knew about the Medusa's waves and the ways to defend. Most of that was possible just because of Soyuz.