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.

Masu arc (9)

This is Masu's story. This arc is closely related to Cecil arc.

This arc is completed.

[Masu arc] [1] [Dandelion] [8618]

Masu arc is about a guy named Masu and much later in this arc, his son will take over. Early stories of this arc are closely related to Cecil arc.

[Masu arc] [2] [Masu the sage] [8631]

This story is where he gains the fame and it is one of few stories that shed light on the Bau from inside.

[Masu arc] [3] [3Ra Syndicate] [8625]

This is actually a side story and is one of very few that deal with the Ra clan.

[Masu arc] [4] [Remorse] [8739]

[Masu arc] [5] [Storm] [8921]

[Masu arc] [6] [The Dietrich] [9012]

[Masu arc] [7] [Wrong legacy] [9599]

[Masu arc] [8] [Dr Anna] [9611]

This story covers a minor character in Dr. Anna.

While not related plot wise to this story, it is recommended to read [Sae arc] [2] [Excessive Sleep Syndrome] [96xx].

[Masu arc] [9] [Demise of a servant] [9649]

This is the final story of this arc.