Ginga no Shinanai Kodomo-tachi e

The story of two immortal children, beginning at the time in which everything has ended. The innocent older sister π that loves to rap, and the introverted younger brother Makki that you can always find reading alone.

The tankoubon chapters are compilated arcs of chapters in the original web release:

Volume One:
Pai - Chapters 1-5
Mira 1 - Chapters 6-7
Volume Two:
Mira 2 - Chapters 8-13
Makki - Chapters 14 Part 1 & Chapter 14 Part 2