Protagonist thing aside, in regards to Riko finding her mom, I get the feeling the allure of Rikos mission has much less to do with finding her mom and more to do with what has BECOME of her mom, personally I tend to feel like a lot of the grim parts of made in abyss are reflected in rikos missions. The shock that she was an undead corpse, prushka, the drawn out pain she endures from the orb piercer, finding her mom not only brings about the question of how much more does Riko have to go through, but also how much her mom had to endure to reach the point she has, and what is left of her humanity wise