At the very beginning of the story, Leon notes that the difficulty of the game was extremely hard and was forced to resort to using a paid item (Luxion) to clear it. Normally it can be handwaved as being a shitty game, but the Marie Route SS reveals that Olivia was possessed by the spirit of the first saint who wants to destroy the kingdom due to her, as of yet unknown, hatred of it. It explains why the game was ridiculously hard and why Luxion, who is established to hate the "New" Humans, follows her as their interests are in alignment.
Luxion's set up of Leon at the end of Volume 5, despite seeming like nothing but Luxion making Leon suffer for his own amusement, was actually in Leon's best interests. If not for the misunderstanding forcing an apology, Angelica and Livia would have been suspicious and angry for their entire stay in the commonwealth as new 'hints' of infidelity came to light. It also helped Noelle to be more easily accepted by the two, where there could easily have been a big rivalry. So, Luxion wasn't just making an excuse for himself at the start of Volume 6.
It may seem odd that in the What If? Marie Route, Leon doesn't get any promotions, despite receiving many in the main story. Then you realize, that most of Leon's promotions were given to him as a way to appease the very aggrieved Redgrave House, who were backing him, and still angry at the crown even after the third volume. Also, the Marie Route version of Leon, with him and his friends having much more favorable marriage prospects, keeps a cooler head and moves with stealth more often than not, as well as succeeding at pushing his fame onto his elder brother, who unlike the five princes whom he tried to push it onto in the main story, doesn't have Honor Before Reason keeping him from accepting it.
Olivia and the First Saint possessing her being fixated on Leon with the latter mistaking him for her true love, the forgotten sixth hero in the What If? Marie route can be a Meta joke when one recalls that several Otome games often have a "Secret Love Interest" route that can only be unlocked after the players have cleared everyone else. Leon, who is later revealed to have been descended from said forgotten hero in this story, essentially becomes the "Secret" love interest for Olivia, the Player Character of the original game, in this scenario.
If Marie's kid didn't get brought over to the new world, it's very likely she's not doing well since both her mother and uncle are dead...
Remember that Marie's daughter is under the care of her grandparents who vowed to raise her right. She'll be fine.
Her grandparents kicked Leon out for supposedly having Yaoi and then kicked Marie out for the resulting lie resulting his death, putting her in a situation where she ultimately wound up getting killed by her abusive boyfriend.
All that being said, The web novel shows that Marie's daughter eventually ended up in that world as a reincarnator. The question is how? And at what age, considering the other reincarnators' point of entry?
This is fairly mitigated by the fact that it's implied that Marie's daughter died old so she is actually living well before her death.
The method by which Leon and Marie wound up in this world in the first place:
In his past life, Leon's death was because of exhaustion due to trying to get back on his parents' good side after his sister's lie by playing the game. But when you consider that it was because they found Yaoi in his room and how his parents responded by throwing him out, how strict were they that just finding that was enough they'd kick him out of the house and force him into an apartment?
And in Marie's past life, her parents immediately kicked her out after her return, ignoring their part in things, and then later take her child from her because they declare her an unfit mother without even attempting to help her otherwise. Her death was literally being beaten by an abusive boyfriend until she woke up in a new world where she has even more blatantly abusive parents.
Given that the royal flagship runs on The Power of Love and Livia and Angelica are able to activate it themselves, one is compelled to wonder whether the original otome game had a secret Gay Option that Leon simply didn't find because he was trying to get his sister the Reverse Harem ending.
