Every time I use my ability, I come one step closer to forgetting everything completely.
Until I save the school beauty I've secretly loved from a monster's lair. Wiping blood from her face, she smiles faintly: "Funny, before my dad disappeared, he said I'd fall in love with an idiot who forgot everything."
Until my civil-servant father comes home late at night with a knife in hand, Lv. 6 monster blood dripping from it. "Time to come clean. Your old man used to be in the top ten on the combat rankings. Tonight, I'll teach you your first lesson in rule-based powers: how to protect everything you want to protect before you forget it all."
Until we discover that the key to opening the apocalypse's gate is the three of us...
My father tears away his twenty-year disguise: "This time, Dad will clear the way for you."
She ignites a forbidden bloodline technique: "If you forget, then we'll forget together."
And facing the ancient gods, I write the final rule:
"No victory may be bought with the sacrifice of someone you love. I'll pay the price myself."
Personally, I think it's okay and the plot doesn't advance very quickly.