All of the main four seem to have gotten their demons in ways related to their demons' Seven Deadly Sins motif:
Maggie gains a demon that symbolizes lust at age 11, which is a common age for girls to enter puberty.
Gil gains a demon symbolizing envy only after his beautiful planet is destroyed, he loses his family, and he is enrolled in a highly competitive boarding school.
In chapter 4 Ava wakes up with bandages on her over her clothes. The person who wrapped her, Gil, says he wants to be a doctor and has been studying for several years now. It seems like a typical example of Worst Aid except we find out his files has him listed as a medical janitor not doctor.
In chapter 17, we find out how much power a pact maker is capable of. If that's what "Wrava" is capable of, how powerful is TITAN?
Maggie's pact with Tuls details that she wants to find someone to love. Tuls mentions that she's tried multiple times before and that they don't have a lot of time left to figure it out before the pact fails. Maggie currently has her eyes set on Gil, and is confident that it'll work out, but Word of God confirms that Gil is gay, so even if she confesses, or uses the Love Potion on him, it won't really count. So, when she inevitably fails to woo Gil, what will become of her and Tuls? They'll probably become that "monster of failure" that Wrathia mentioned before, and even someone as mean as Maggie doesn't deserve that...