This rather lengthy update will focus on some of the gameplay aspects of Tristian. More specifically, their classes. But first, a quick breakdown as to how characters living in this world gain their abilities:

Magic:

As magic in Eridanus is an extremely rare practice, little to no true magic users will join your party. True magic simply implies, in videogamespeak, a character that learns magic while gaining levels, aka the traditional way. There was exactly one character in the old demo who could learn spells this way: Dante.

Ianna can only learn magic by equipping tomes or by learning new spells from skill orbs. These skill orbs are manufacted using the Crysali that the player randomly finds scattered throughout the world map, or as drops from elemental fiends. However, this way of gaining skills isn't only limited to Ianna. Virtually any character who has a half-decent magic stat will be able to use these skill orbs ( I need a better name for it, seriously ) to cast the spells associated with them.
Naturally, these spells are far weaker than their original counter-parts, but make up for their lack in firepower by adding status effects or chip-damage for characters with weaker ATK stats ( like Ianna and Darcy).

Furthermore, some magic-imbibed weapons ( only obtained in Connaught's captial and the game's first town, Enoun ) can also grant new abilites. However, due to their scarcity, they are quite expensive, so it is extremely unlikely that the player will be able to obtain these goods early-game ( or much later in trade towns such as Concordia Port, as seen in the old demo ).

Princess:

A magic-wielding class with access to powerful healing and light-based spells. Becomes a powerful Queen towards game end

Ianna's gentle nature naturally lends her to learning support and party-healing skills, but her thirst for magical knowledge allows her to cast spells from magic tomes. Later down the line, she asks Tristian if the knight can't teach her the basics of swordplay, which allows the young princess to equip light swords and ones of the magical variety. Although not a true-magic user by birth, Ianna's lineage allows her access to the Light-based magic of Dubhan ( who was previously aligned with Dark-magic in the older demos ).

Physical Skills/Abilities:

This is somewhat tied to character classes, so I'll kill two birds with one stone here. I'm also trying to tie a character's specific skill set with their personality.

Battle Skills are by tradition, taught by the various military schools scattered through Eridanus, though the best ones tend to be situated in Genoa itself. Squires training to become full-fledged knights either follow a discipline in offensive or defensive abilities. Most military skills tend to be linked to the trainee's weapon of choice as well, and require a certain degree of proficiency with them. It explains why Percival cannot learn any weapon-based skills, nor can Tristian learn any of Edmund's lance-based ones, despite the fact she can equip lances upon promotion.

Paladin:

A offense-based class with some turtling skills and low-level healing magic. Can either promote into a Templar or Master Knight.

Tristian's abilities centers around her equipping specific weapons to access her varied skillset of damage-based skills. Her Cover ability nullifies damage taken for the entire party, but at a price. Because the lady knight decided to study weapons-based fighting at Liguria Academy, she is more proficient at wielding weapons than her brother, Sir Percival, but her protective nature still allows her to shield her allies.

As a result, she has access to both the Templar and Master Knight classes upon promoting.
However, as an Infantry unit, she is weak against thunder-based magic and Anti-Infantry weapons like armourslayers and crossbows and her prideful nature actually limits some buffing techs only to herself ( such as Lionheart ).

Dux Knight:

A defence-based class centered around buffing and equipping heavy weaponary.

Unlike his sister, Percival is the opposite when it comes to encountering foes. He will rather defend the group with a wide variety of party-buffing/enemy-neutering skills, as he is none too comfortable to wield weapons to the degree of Tristian ( in battle, he is more likely to miss his attacks ). His quiet, pacifist nature lends him to be the 'strong, silent type' but he still has a formidable sword arm if the situation calls for it.

He promotes into a Duke Knight during the course of the game, inheriting the title of Duke of Reglay as well as gaining an array of more powerful techniques. Like Tristian, Percival is vulnerable to Thunder-based skills and anti-infantry weapons.

Dragoon:

A lance-locked class with devastating abilities. Already promoted.

As the game's sole Dragoon, Edmund has access to the most powerful offensive skills, even if he can't Jump. He lacks Tristian's all-round abilities and Ianna's healing, but more than makes up for it in sheer destructive power. All of Edmund's lance-based skills are Piercing and can inflict the Bleeding status.

I'll probably halt the update here, lest I bore you all to death since the update clearly does not contain any TristianxIanna goodness.