Granblue Fantasy is a hugely successful franchise that has been killing it in Japan since its release in 2014 with over 25 million current downloads. The game isn't available in the states through normal means, but hasn't stopped American fans from getting their hands on it too. The franchise has since transcended genres into the fighting game sphere and that's also crushed the goals it set it out to accomplish.
With that said, there's one more character to be revealed for season 2 of DLC for Granblue Fantasy Versus, and it's possible season 3 is coming. There're so many loveable (and loathsome) characters in the franchise that would be more than welcome as new DLC.

1. Eustace

Eustace from Granblue Fantasy
Starting off, Eustace would make a great addition to the game because he's a character that uses guns in the original Granblue Fantasy mobile game. There're no characters yet in Versus who use guns, so his gameplay would be fundamentally different from anyone else's.
Eustace is also seen with Vaseraga and Zeta often who are already in Granblue Versus, so he'd fit right in with the cast for a story mode chapter of his own. His unique skills from the mobile game would make for unique interactions and game mechanics on top of his gun usage, so he would make a fine addition as DLC.

2. Siegfried

Siegfried from Granblue Fantasy
Siegfried is the leader of the knights who saved his country from great peril. He has huge lore significance and it's almost shocking that he hasn't made it into the game yet, unless the developers are saving him for season 3 of DLC.
His unique abilities allow him to buff his own defense and lower the effects of debuffs cast onto him. This could translate to a unique playstyle focused on buffing his own defense or granting him armor similar to what Vaseraga has. He has 3 different skins in Granblue mobile that have varying degrees of armor covering his face, so the visuals from those skins could translate to this mechanic.

3. Sen

Sen from Granblue Fantasy
In Granblue Fantasy Versus right now there are only 2 characters who fit the melee category and there's so much room for more. Sen would be a great addition since her skills focus around dodging and counters that buff her damage and evasion. The other melee characters are grappling and tough, which makes them hard to deal with up close.
Sen could play like a rushdown type character who zips in and out using her dodge to bait opponents into making punishable mistakes. Her cat-based techniques would also be refreshing to see when contrasted with the flashy dragon and god summons of the game.

4. Vira

Vira from Granblue Fantasy
Vira plays an integral role in the story of Granblue Fantasy and is a fan favorite from the game's early days. Her abilities change across her many forms, but she has unique mechanics that haven't been introduced to the game just yet.
A big example of a unique mechanic is her life steal ability. The ability to steal life and do damage to an opponent is something pretty common in fighting games, but difficult to implement in a fair way. It would probably have to be attributed to her Skybound Art so players couldn't abuse it.  Lastly, she could use the Primal Beast Lumeneria to summon small helpers and have them appear in her Super Skybound Art.

5. Sturm

Sturm from granblue fantasy
Sturm is a mercenary who finds herself working with the empire until being recruited by Gran in the main story of the mobile game. Her ability with a sword is nothing to laugh at and her skills in combat grant decent buffs in battle.
She would make a great candidate for DLC since she's very recognizable, but her abilities aren't that unique. Translated into a fighting game, she would most likely be a character like Soriz who unlocks her Dual Blade ability as her Super Skybound Art, which would buff her attack and maybe give access to new moves.

6. Beatrix

Beatrix from granblue fantasy
Beatrix is another fan favorite who belongs in the game considering the love her fans have for her. Her skills allow her to boost damage by landing certain moves and building them up through Delta Clock.
Since Delta Clock is activated by the amount of triple attacks, she could have a combo ender that has different levels of strikes. The light attack would be one, medium two, and the EX slash would be her triple strike. Build up enough triple strikes in a game, and she would be able to do more damage than normal.

7. Tweyen

Tweyen from granblue fantasy
As Granblue Versus stands now, there's only one bow user in the game, so zoners don't have too much to go off of for character selection. Tweyen would make for a great addition to the cast as a fully dedicated zoner who controls the screen from long range.
Tweyen is an Eternal with unmatched power who is also extremely skilled with a bow. Her selling point as a fighting game character is her Depravity skill. Depravity inflicts random debuffs on her foes and would make for an interesting mechanic in a fighting game. She could posion enemies, stun them, lower their defense, anything along those lines, while staying unpredictable the whole time.

8. Baal

Baal from granblue fantasy
Baal would be an extremely interesting character to add to Granblue Fantasy Versus because he is a harp specialist. As of now, there're no harp specialists in the game except Yuel, who also can use katanas. Baal's style generally focuses on buffing his allies as well as debuffing enemies.
Baal could play like a mid-range zoner that negates certain zoning capabilities of other characters like Metera or Ferry. A character that can set traps while controlling the enemy's movement is a frustrating playstyle to deal with, but very rewarding to learn.

9. Ilsa

Ilsa from granblue fantasy
Ilsa would have a very unique intro since she likes to yell and act very strict. Her introduction to her opponent would be stern but caring, to encourage improvement. She also uses a gun so that would bring unique elements to her gameplay since nobody does that yet in Versus.
Her Bullets system would translate very easily into a fighting game with her having to reload to do certain moves, or buff her combo damage.

10. Sandalphon

Sandalphon from granblue fantasy
Sandalphon is one of the most popular characters in the Granblue Fantasy franchise who also won a popularity poll for characters to be added in Granblue Fantasy Versus. He has the ability to control opponent's elements and also can fly with his four wings.
He has so many unique mechanics to himself that he would make an easy transition into the fighting game and probably be one of the more complex, and hopefully, powerful characters. He's extremely likely to make an appearance due to his popularity so definitely keep an eye out for him.