Blame procrastination for not doing concepts for so long. Finally had the motivation to another one and actually complete a concept. I decided FE as that would keep me motivated to work on the concept. It’s a bit bad after having not doing any concepts for very long. Anyways, let’s get to it.
This concept has heavy spoilers regarding Lysithea’s backstory and some about FE3H plot so view this concept if you wish to.
If the description is too long, I apologize, there are many key characteristics of her that I couldn’t ignore, and additionally mostly used in this concept.
Summary
Lysithea von Ordelia
Source: Fire Emblem Three Houses
Description: The sole survivor of the blood experiments committed by TWSITD, she bears the Minor Crest of Charon and Major Crest of Gloucester, but her lifespan is shortened dramatically. Lysithea resides in Garreg Mach, she seeks to finish her education, and to settle all of her family’s affairs. Although, she has been treated like a child with her sweet tooth side and her fear of ghost.
Quote: It’s clear my body has succumbed to the intense pressure of bearing two Crests. Due to the immense requirements of bearing these Crests, my life expectancy is…painfully short.
Role: Damage
Position: Back
Stars: 
Trial Team: Red
Animations:
Basic Attack: Lysithea sends the spell Miasma Δ at a single enemy.
Entrance: Lysithea walks in while reading a book, and puts it away after.
Victory: Eats a sweet then goes back to reading.
Defeat: Lysithea sees a ghost and runs away.
Skills:
White Skill: Luna Λ
(Fantastic Damage 
)
Lysithea deals X damage to the enemy with the most HP additionally, bonus damage equal to 50% of that enemy’s Reality. This also does X damage to nearby enemies and bonus damage to those enemies equal to 10% of their Reality. This also stuns any enemy hit by this skill by 2 seconds.
Green Skill: The Divine Essences
Lysithea takes out a sweet (Cake), and eats it for 3 seconds. Lysithea heals X HP, and gains X Damage and X SP for 5 seconds. If Lysithea is hit while she’s eating, she’ll give it to an enemy by throwing it, healing their Max HP by 15% but are silenced for 7 seconds.
The cooldown of this skill is 9 seconds and starts when the animation is done for either outcome.
Blue Skill: Perfect Comprehension
Lysithea pulls out a book, and starts reading. The 3 most frontline enemies are Studied for 7 seconds. She gains 20 Fantastic Crit, and is buffed by X SP for 6 seconds. This occurs every 9 seconds.
Purple Skill: Mastermind
Lysithea deals X more Damage to enemies who are affected by Studied. Lysithea also gains X SP for 7 seconds if an enemy that is Studied is KOed.
Red Skill: Duel Crest Bearer
Every time Lysithea uses her white skill, “Luna Λ”, she has a 60% chance to gain X Damage and X SP for 8 seconds. She’ll also decrease the enemy’s Reality by 20% that was directly hit by her white skill for 6 seconds.
The chance of this skill activation is decreased if Lysithea is above Level X.
Stat Boosters:
+X SP
+X Reality
+2 seconds of “Study” in “Perfect Comprehension”
Friendships:
Lysithea and Rapunzel
Disk: Wonders of The Outside
Debuffs are able to be cleansed
Campaign: Appreciations of Life
Description: Rapunzel talks to Lysithea and learns about her shortened life span and Rapunzel decides that she’ll need to make the most out of her life. Rapunzel decides to talk to her into being more outside and to be more adventurous. Lysithea wishes to continue studying instead but Rapunzel is determined to convince her.
Ending: Rapunzel and Lysithea decide to cook and bake together after a long day.
Allies: Flynn Rider, Collete, and Joy.
Lysithea has a 10% chance to cleanse all buffs when she uses the skill ”The Divine Essences”. (+5% per star)
Stat Boosters:
+X SP
+X Reality
Lysithea and Ralph
Disk: Rewarding Treat
More Energy Gain at the start of the fight
Campaign: A Sweety Find
Description: Ralph finds that Vanellope has gone missing, and can’t find her anywhere. Lysithea and Ralph decide to do an exchange with each other after hearing about Vanellope and her association with sweets.
Ending: Lysithea and Ralph learn that Vanellope was looking for Lysithea after learning of her love for sweets. They both talk and exchange sweets afterwards, whilst Ralph leaves them to it.
Allies: Felix, Swedish Chef, and Bolt.
For the first 5 seconds of the fight, Lysithea gains “Energized”, and gains 65 more energy. (+1 second per star)
Stat Boosters:
+X Damage
Costume:
Additional Notes:
“Sweets” is not specified in the game.
Regarding the silence part in her blue skill, this is a reference to her C support with Felix. Lysithea pays Felix for silence about her eating cake.
The “Divine Essences” part of her Green Skill is referring to the quote in Felix’s and Lysithea’s B support.
Lysithea’s costume is her post-time skip outfit.
TWSITD = Those Who Slither in the Dark (Agarthans)
In her epilogue by herself, she does indeed end her family’s affairs.
Mastermind is her personal skill in FE3H, and regarding the buffs in her Red Skill, she is able to do more 5 more might with Magic Attacks with Crest of Gloucester and 5 more might with Combat Arts with the Crest of Charon.
Lysithea is scared of ghosts.