The avatar is your own customizable character in the game. The appearance you'll set will reflect on your character's 2D portrait in dialogues, sprite, and 3D model during battles and cutscenes. The customization option isn't too extensive; however, it's broad enough to give players distinct avatars.

You can choose your avatar to be male or female. Each gender has two body types (short or tall) and per body type, you'll have access to 7 faces and 12 hairstyles. There are 30 hair colours regardless of gender and 5 hair accessories available only to female characters. Finally, there are 12 facial details (like moles, facial tats, eyepatches, etc) and 3 voices (5 in the Japanese version)

Before completing your character, you'll get to set his/her birth month, birth day, Boon, Bane, and Talent. These selections have permanent effect to your character for the entire gameplay (or until you create a new one or edit your original avatar when trying out other routes) so careful consideration is needed for this.

Birthdate
I haven't seen the bonuses to the avatar on the day itself but your other characters who celebrate their birthday will get the following bonuses:
Boon and Bane
Boon is your character's strongest stat. It also increases faster and has a higher cap. Bane is the opposite; this becomes your character's lowest stat, increases slowly, and has a lower cap. Consider these two things during character creation as they'll be permanent until you start a new playthrough.
| Affected Stat | Boon | Bane |
| HP | Robust | Sickly |
| Strength | Strong | Weak |
| Magic | Clever | Dull |
| Skill | Deft | Clumsy |
| Speed | Quick | Slow |
| Luck | Lucky | Unlucky |
| Defense | Sturdy | Fragile |
| Resistance | Calm | Excitable |
Character Classes
The default class for all avatars always starts as a Nohr Prince/ Princess. The advance class will depend on their affiliation, either has a Hoshidan Noble or Nohrian Noble. From there, the avatar will have a very flexible list of options to re-class with the help of support ranks and seals.
First off, the avatar can use a Heart Seal to change to a secondary class based on the Talent you selected for him/her during the character creation process. If you're already a Noble (an advanced class) then you can also select the advanced version of the Classes listed below:
Apothecary
Archer
Cavalier
Diviner
Dragon (Wyvern Rider)
Fighter
Knight
Lancer (Spear Fighter)
Mage (Dark Mage)
Mercenary
Monk (male)
Ninja
Oni Savage
Outlaw
Priestess (female; Shrine Maiden)
Samurai
Sky Knight
Troubadour
Alternately, the avatar can re-class to his/her partner's base class using a Partner Seal or the base class of characters which the avatar formed A-rank supports with using the Friendship Seal. Unique Classes like the Songstress can't be acquired by anyone, including the Avatar.