(Damn this is long, just skip to the end if you don't want to read the whole explanation)
Okay so we know that Alastor was gone for 7 years and judging by the conversation with Zestial nobody knew where he was.
And then it was revealed that Rosie was the one who owned Alastor's soul and sent him to wherever he went. Therefore making her and Alastor the only people we know of so far who knew where he was and why he was there.
But the thing is...
Sinners can't leave the Pride Ring.
So Alastor would've either have had to have still been in the Pride Ring, which seems highly unlikely considering that, again, nobody knew where he was except for Rosie(even Vox, who has been shown to have cameras all over the place, isn't shown to know exactly where he went) or he left somehow with Rosie's help.
But isn't Rosie like, also a sinner? How would she have the power to send another sinner outside of the Pride Ring when she can't leave herself?
Well, Rosie is shown to be way more powerful than any of the other Overlords. Like, she was the one who granted the strongest sinner in hell his powers. How would another sinner have the power to do that?
Well, I've recently seen this theory online that Rosie is either Roo or Lilith in disguise, and that actually makes a lot of sense considering how much power Rosie has and that they all wear the same hat for some reason. Not to mention the theory that Roo is Eve. Maybe they're all the same person, who knows at this point?
I know I'm just saying stuff other people have said at this point, but trust me it's all important for my theory.
Okay, so let's recall the exact words of Alastor's lament to Rosie.
"Fruitless crusade."
Now this could be Alastor knowing that Rosie is Lilith or Eve and making a jab at her,
Or it could be a reference to what Alastor was looking for, which makes a ton of sense when you consider Rosie's possible secret identity.
GUYS I THINK AL WAS TRYING TO FIND THE GARDEN OF EDEN.