I'm working my way through and I'm thinking about FFS's question 4: Why does Oric want the Target dead? This is supposedly answerable in the first chapter and a half, specifically it was announced during the Megaman Arena Battle.
First, lets look at when Oric and Ciro meet. This is the only known direct quotes we have from Oric. Oric is sarcastic to Ciro, condescending to Spira, and focused on searching out the level. Spira accidentally lets his name slip, Oric is angry that he has to act like a villian the whole time, and tells Ciro not to follow him. He stops Ciro with some sort of magic, and when Ciro asks about his origins, Oric begins with a wierd prison analogy. People have interpreted it as meaning Oric is recreating his original prison in his warrens. This is wrong.
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"You know where you are going, but you don't care. You have been trapped so long you know only the cell. Exile is escape, Punishment is reward." Oric is no ruler at all. He's stuck here just the same as every joe schmoe. Riltia says "recreate the prison", but that does not mean he is free. She also says that she would know him if she worked for him, although as Ciro's rebirth amnesia proves it might take a major experience to reclaim those memories. I'd relate it to a slave-era taskmaster where a slave would be given the task of making sure the others kept up the good work, thus getting hate from both sides. The Mechanic, Eye, and Voice are on board, while the others must be potentially negative to the current order. Spira obviously isn't able to control Oric, thus neither is Betweenford if he has a similar power level. So why does Oric want the Target dead? Answer: His bosses told him to. The same reason he locked up the Rebel for mucking up his bosses' plan by killing the important pieces.
Now, the real question is if we have to answer who/why Oric's bosses want us dead. My first instinct is that they are the enemy of Betweenford and co., thus why we have regularly had help from them. Perhaps they are supposed to be the angels, but their interference allowed Riltia to spawn neutral if not friendly to Ciro. This also makes me wonder if Ciro is supposed to be the boss of DL7, and that DL8(+?) belongs to the mysterious masters that set the whole thing up. Perhaps we are the only ones capable of taking them down by uniting the siblings. Perhaps we are the only ones capable of Oversoul, which is why we can take on the masters.
Wait, looking at blue/betweenford, they mention taking betweenford back to the oversoul to heal. So their boss is Oversouled. Perhaps us going Oversoul took away power from the ruler/master of this place. Maybe that was what allowed the Rebel to break free, and the fact that it ended early was because we voluntarily gave up our power to Riltia instead of it winding down another way. Just because it happened before doesn't mean Ciro got anywhere. Especially with limited memory. By telling all the other siblings to take on the target (except rebel for fear of "friendly fire"), perhaps they are trying to separate and eliminate the siblings
Note: I am posting before getting to chapter 3 so newer events may contradict my theory.