Board Thread:Questions and Answers/@comment-209.95.32.55-20150909070610/@comment-30575144-20150909115733

To enter burst mode, you can either press R+Triangle at the end of your combos (I use B type controls) or hold triangle till the god arc head is formed and release triangle to devour a active aragami.

there are other ways too... also if you have a character like Alisa (new type God eater) they can trigger a burst through link burst.

as for blood rage you must clear the game past rank 8 to use it. also note there are tutorial in the game that tell you how to do this.