In volume six of Chrono Crusade, we get a lot of backstory as Rosette voyages through the dangerous environment that is Chrono’s mind. This is an especially dangerous procedure because of their contract. There is a very real danger that Chrono might accidentally eat her soul. (Rosette of course does not care. She just wants Chrono to wake up. If Rosette had any sense of self-preservation, this would be a much shorter manga.)
We see the Sinners, circa 1870, in Northwest Arizona. Chrono and the other Sinners are at the Grand Canyon. They have recruited a young human woman named Mary Magdalen to find a certain object. And by recruited I actually mean, “kidnap.” (Though this abduction it is the strangest kidnapping ever, since Mary actively assisted Chrono in escaping from the Magdalen Order.) Mary’s abilities are the ability to see into the future and the past, communicate with the dead, and the ability to see at a distance. These are all very useful skills to have when you are attempting to find Pandaemonium’s head!
Because of Mary’s fearlessness and willingness to help, the Sinners are quickly charmed by Mary! Especially Chrono, who follows her around like a love struck puppy. Aion thinks this is the funniest thing ever, and there is a great deal of brotherly teasing amid some very lovely domestic interaction. Rosette seeing this can’t help but be touched by it.
Unfortunately, things go very wrong when Pandaemonium manages to regenerate and attempts to attack the Sinners. Pandaemonium is eventually defeated, but Mary becomes possessed by Pandaemonium’s spirit. Aion realizing this, goes into a panic and orders Chrono to kill Mary. (Mary in return seems to have expected this to happen, much to Chrono’s horror.) Chrono tries to talk Aion out of this, but Aion decides to interpret this as insurrection and betrayal and attacks Chrono.
This leads to Chrono and Mary being on the run. The plan seems to be, ‘get to the Magdalen Order and hope they can help.’ The plan however, falls through when Aion catches up to them. (Interestingly, Shader accompanies Aion and gives Chrono the device that seals his powers.)
Rosette witnesses this and eventually confronts Chrono inside a space that looks like Mary’s tomb. Meanwhile in the real world, this soul-diving trip is taking a toll on Rosette. This leads to Ewan shouting at Chrono about how he shouldn’t give up. (At sword point.) Chrono eventually wakes up, mostly because of Rosette kicking him in the hiney with how much she cares about him.
Now that Chrono has reaffirmed his intention of protecting Rosette and Rosette has more or less handed him her heart they can go off to rescue Joshua. What neither of them know until it is almost too late, is that Ewan has been issued an extermination order for Chrono, who has been judged “too dangerous to live,” by the higher up members of the Magdalen Order. (Once again, a group of authority figures has decided that solving a problem by disposing of it is the only answer to the situation.)
Fortunately, Ewan knows when to act on his own conscience and he decides to turn his execution order into a very rough sort of tutorial for Chrono. The gist of the tutorial “do not just get angry, you moron, THINK.” This lesson is very much taken to heart, though you can bet Chrono is going to be doing more stupid things in the next volume.