Both of these were a part of GE:Resurrection (guess where that game got those from, heh). Skill effect varies depending on their level and low levels could be improved into a higher level by stacking two of the same skill.
With these, it's possible to install these Arcs' abilities into equipment.
Raising a Blood Art's proficiency requires going on newer missions and completing it, thus finishing a mission with a higher rank gives more experience points to the currently equipped Blood Art, as well as the other Blood Arts of the same variant. Blood Arts are an "attack add-on" that can augment normal attacks of all manners into an even stronger attack, thus making it either unlock new Blood Arts, or convert existing one into a much stronger variant. Blood Arts: The "Blood Arts" are one of the new additions in the game.You can see it being activated and used against an Aragami here! Temporary invincibility can be toggled during the pledge selection process, at the expense of draining the Awakening gauge.
God Eater: By manipulating the "God Arc" which incorporates the same "Oracle Cell" as humanitys natural enemy Aragami, they are the only ones who can defeat the Aragami. Members of the Special Force (pictured above) along with yourself - the protagonist in this story - are sent to investigate and exterminate the creatures that bring destruction to our planet: the Aragami, and to discover a way of preserving and saving the remains of humanity. A new fatal pandemic named Black Plague strikes the Far East Branch and the mortality rate is of 100%. Set in 2074, 3 years after the last events of God Eater: Resurrection.