Need help with doom and destiny advanced

I'm at ch 12 were the dark Eidous said for 450 but I'm at 400 after buying the void case and now I 50 more,Idk what to do to increase it is there a area I can go to get more,side quests that increase it,or someone that can give me a quest to get?

Pls I need to know because i really like the game a d now I'm stuck here.