Reili
You know with this her sword should be one of if not the strongest weapon in existence all the whole it's in an incomplete state honestly I can only imagine how powerful it will become as the runes of destruction on the sword are incomplete but given she reaches rank 5 in divinity with destruction and Creation she should be able to greatly improve it again then if you add on to the fact that the runes already on it were only at 3 percent completion that was supposed to be for space and time manipulation and finally adding an true immortal soul like the Ancient Terror that represents corruption that goes perfectly with destruction also not to forget it has Error's power as well with various elements and nanobots. Shiro's sword at that point would likely be capable of tearing apart space and time striking at the source code of all beings while bringing them to null if they survive that somehow they would be corrupted and would end up serving Shiro. So yeah it's going to get op real quick.
I have only one concern about Arnea - Shiro ask her to be her bodyguard why she didn't take Lissandra for that? And help her level up? Lisa already represent destruction Shiro needed. And she defenetly much more powerful than Arnea,because she is demigod already. Looks like Reili tired of party members somehow and decided to send Shiro into solo journey (like all of those quests before). In reality, if Shiro go out with someone of her party, it always look more joyous and connected to the main storyline then she just met some random dudes and go with them.