For lack of a better word, her tits look great! Good job!

Compare Mara's earliest pics with this one.... why do artists endlessly dumbly enlarge the breasts of their girls?
This breast size is even bigger than her mom's and her aunt's. That is definitely not cool.

first off, this is not Mara. It clearly states that it is Vtuber Mara. A fake sci-fi digital representation of her. Big tits are part of the appeal to get views.

Secondly, it was repeatedly stated that mana is stored in the breasts. The more mana they have, the more the breasts grow until said mana gets used up. It's a natural progression for anyone living for an extended time on the magical side of the world. For Mara, that's around 10 years of traveling with Jake until they travel to the modern side. Mara's family members would be much larger than they are if they had been for that long over there or had been in a relationship with Jake for a few months.
(You should've noticed that Mara's breast size is inconsistent between images because of that. Sometimes they're large or even massive, sometimes they're the average she has had for years. But at the end of the day, it heavily depends on what I am in the mood for)

yoo ScorpDK, thank you for such a detailed and refining response!
I also should have mentioned that the posture, facial expressions, and swaying hips with a tail are pretty darn cute! ^^

Gawd damnit, this is good >:3c

it was only a matter of time before Mara discovered OnlyFans XD