Desiree

Concealed by Desiree's juvenile, perky appearance is a past filled with hardships. The orphanage where she once stayed was a poor excuse for a sanctuary. Before she was adopted by that mercenary organization's member, she barely even got to have meals that tasted normal.
The demanding training that awaited her at the mercenary organization didn't really faze her. As her "teachers," the organization members taught her all the qualities and knowledge needed to be a soldier, albeit not exactly with care and concern as the intention, but they did shape a complete "worldview" for Desiree, granting her basic understanding of this world.
However, on the flip side of the coin, although the "teachers" cultivated her into an impressive mercenary, they failed to teach her the skills needed to live independently. As such, till date, Desiree lacks budgeting ability and requires the supervision of a "guardian."

When Desiree first boarded The Eternal, the first impression she gave everyone on the train was "a girl who possesses some combat skills" and even "perhaps a relative of someone." After all, no matter if it's her looks or behavior, she exudes the naivety of someone without much life experience, which makes it difficult to imagine what kind of amazing abilities a girl like that could possibly have.
Regardless, this somewhat stereotypical first impression was soon proven wrong.
Desiree is proficient at moving between numerous spots to quickly find a good one to snipe, then accurately taking down the enemy. People skilled at using long-range weapons are generally seen as the team's attacker and weakest member, but no one who has seen Desiree using the advantage of her petite frame to swiftly block and knock down an enemy would think she had gotten her position by pulling strings.
About her astounding abilities that starkly contrast her appearance, she doesn't appear to have much thought about them, never mind comparing herself with others. In her eyes, everyone has their own individuality. For example, Livia makes extremely good Black Tea, Eliot always invites Desiree to play, and Fran cooks for everyone... Desiree has never felt that her existence is "unrealistic." She still spends her days happily on The Eternal, just like the saying, "Ignorance is bliss."

A crew member found a notebook and handed it to Livia, hoping she could locate its owner through its content.

Page 1:
Conductor told me to write a diary since I am bad with words and writing reports.
Fran said as long as I keep writing, I will master it one day.
I wanna try!

Page 2:
So hungry! Not sure what to write.
I want a refreegeerater (splotch of ink) (a vertical rectangle with a horizontal line across the middle) Everybody always makes yummy food from the refreegeerater.
(doodles of a bunch of odd stuff, may be mistakes)

Page 3:
I ate a burger today. It is yummy. Could have had 3 more, but Kersed Sword Maiden ate them. Found 2 bentos and gave them to the Conductor, but the Conductor gave me 1 back.
Left all the green peppers for Conductor.
Also scared the fancy passengers in the passenger car. It was fun.

Page 4:
(oil stain) (oil stain) I love bentos!
abcdefghijklmnopkrstuvwxyz (written in one crooked line, as though using the hand that's not holding the spoon)
1 bento box
5 sock. 1 missing?
No idea. A dropped arrow on the floor.
(oil stain)

Page 5:
2 bento boxes
(doodle of a weirdly shaped person meant to be Conductor, with a smiley on the side above the head)
Conductor praised me last time. Yay... I wanna play again!

Page 6:
3 bento boxes
Yummy!!!
I could not spell some words, so I went to ask the Conductor and Livia. Livia said I can ask BOX if they are busy.
But I wanna play with them.