Medal Rank

While you are going through the different missions, you will be collecting . These orbs increase your score, and also increase your rank in the stage.
Rank might not seem important at first, but it really is. With higher ranks, comes greater rewards for finishing the mission.
Look at the image to the left. This is the icon found in the top left corner of the screen. This shows you what your current ranking is in the mission you are on. When you collect medals, the yellow ring around the edge will begin filling up. When it completely encircles the rank icon, it will raise one rank.
As you increase in rank, you will earn greater prizes. Also you can get special attacking scenarios. A lot of the time, reaching Rank S will net you a attack that just destroys everything on the screen without hitting it. These special attacks are not a constant for the different ranks, but are frequent.
If you are hit, you will lose exactly one ring of the outer circle, which drops your rank by one. It is best to do your best to avoid collisions with enemies and objects. Below is a complete list of the 25 different ranks you obtain while collecting medals.

Rank 1	Rank 2	Rank 3	Rank 4	Rank 5
Rank 6	Rank 7	Rank 8	Rank 9	Rank 10
Rank 11	Rank 12	Rank 13	Rank 14	Rank 15
Rank 16	Rank 17	Rank 18	Rank 19	Rank 20
Rank 21	Rank 22	Rank 23	Rank 24	Rank 25

Rank Trophies

If you can reach Rank D-S, you will be given a special Rank Trophy for that mission. Below are the different trophies you get for the rank you accomplish.