El Shaddai: Ascension of the Metatron

Here is a very easy methode where you just grind red orbs by destroying objects:

Select Mission 11 on Easy (the red orbs are more effectiv on easy) and the normal armor.

As soon as the level starts run through it and destroy ever red crystal you see, after the half of the level you can pick up a gale to speed up.

There a three forks in this level, at the first one go the right, at the second chose the left (red flame) and at the last one the right to destroy all red crystals. When you reach the bridge where the screen changes the color from red to grey run back to lucifer and save (otherwise the game woud nout save your progress). Now start the level again and repeat this until you got your boost to level 10.

Quote by burymagnets: Actually the autosave when you come up against Azazel will save your boost level just fine, you don't have to go back to Lucifel at all.

By collecting red orbs in each level (especially the bigger ones that you find hidden in pots and in hard to reach places) you will slowly increase your Boost level. The game won't inform you when your level increases so if you're curious you can just hit Back and check it out on the right side of the screen. I was a little ways into my third playthrough of the game when I reached level 10.

Here is just a little to add to Zacry072's solution:

Considering you are going to need at least 2-3 playthroughs to get this, I found a nice little area to boost this as well. After you have finished the game you can select any chapter that you wish. Do the following:

---Select new game
---Select Easy
---Select Chapter 5
---Select Normal Armor (you will NOT get orbs from the enemies wearing the "Special Armor")

Work your way through the level and when you get to the side scrolling section of the level, back out and repeat. Keep doing this and you will eventually get to level 10.