Don't know where to begin?

While ultimately it doesn't matter which arc you begin with, Cecil arc is recommended if you want my recommendation.

And then Masu arc + Shattered union arc. 

Feel free to visit the lore section as well which holds stories of its own.

Hermit arc (3)

Ssil's story, who is a class S ESP.

She's also the leader of the Gypsies.

[Hermit arc] [1] [Sslien] [9488]

This arc revolves around with a class S ESP Ssilen and the Gypsies guild.

[Hermit arc] [2] [Serenade to Death] [9488]

[Hermit arc] [3] [Moon refugees] [9637]

Karveel makes his second appearance in the story. His first appearance was in [Shattered union arc] [6] [Fraser's Regime] [9614]. He isn’t a guy who has a bigger role at this point however…

Related story : [Kain and Suu arc] [7] [Valid concern] [9636]