Otouto Ja Irarenai!!

弟じゃいられない！！
Artist:  Minaduki Yuu
Language: English
Download:
Chapters 1 to 5 from Kagerou Scans
Chapter 6
Extra

Summary:

Kai loves his step-brother Riku from the bottom of his heart. However, Riku treasures “the bonds of sibling hood” more than anything, so Kai must hide his feelings and instead act as a “good brother” but just skin ship no longer satisfies him!

To support the mangaka and buy on Amazon Japan:
One Volume