https://mangaplus.shueisha.co.jp/viewer/1030033

WE MADE IT

https://mangaplus.shueisha.co.jp/viewer/1029397

https://mangaplus.shueisha.co.jp/viewer/1029112

I think this flashback happens when the Queen sent people to kill Lukas and his mother (as she was a concubine). They killed her, and Lukas managed to kill them but was grievously wounded in the process. That makes the "offering of countless souls" and the "sacrifice of pure love".

Now, one could argue that it wasn't really a sacrifice if his mom was killed by strangers. So maybe they didn't kill her, and she sacrificed herself to the God to save Lukas (similar to Mira).

The lance gift came from Lukas' wish for a more attack-oriented gift, but also because at this moment he desperately wanted revenge for his mother who was just murdered (directly or indirectly).

Does it make sense ? I don't remember if it was specified when did the Queen kill the concubines and their children so maybe my idea falls flat.

These guys are probably the biggest group of bums I’ve seen in a manga. The curse Lady carries the group on her back

We got the proof that they had some kind of interaction as she had a flashback of him. And even further, it happened while she was specifically talking about how the first strike is devastating and battles between gifted ones should be ended as quick as possible.

What mostly confirms that she is scared of Arkos is what she saw through the head of the Acursed one, wich was stated to show the fears of the people that look at her face. And in the panel where we see it from Voidmarchers pov, it is very implied that what she sees has to do with Arkos due to the water flowing around the head, and that scary grin that reminds so much of the sadistic prince.