Honestly, it makes sense that Lucas is the end game.
He was always there for Athy. He always helped her with mana and taught her magic.
Had it been not him transporting Athy to Ijekiel as a fun they wouldn't have ever met until debutante.
He even told her about the World Tree Branch to save Claude. Although he didn't want to tell her this earlier for fear of losing her.
And even that prophecy Athy has where the whole nation is in ashes. And Lucas figures out that it might be because he will end up killing everyone until nothing but ashes are left in the nation if anything were to happen to Athy.
He is a mix of Tsundere and Yandere :3 but a great mc.
Oh my god I hate that butler so much, ugly bastard inside out. Rotten to the core. I would rip his dick out if I could. Agh