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.

Milk way arc (5)

A tragic story.

This arc is completed.

[Milky way arc] [1] [The beginning of tragedy] [9613]

[Milky way arc] [2] [Voiceless scream] [9613]

[Milky way arc] [3] [Flawed system] [9613]

[Milky way arc] [4] [An end to many] [9613]

[Milky way arc] [5] [Blissful death] [9613]

This is the last story in this arc. If you’ve come this far, I am sure you’ve read its related stories I’ve thus far recommended. If not, you need to go through them.