My Younger Stepbrother Can't Keep His Hands Off Me!

Yukio Tanikawa always wanted a cute younger brother as an only child to a single father. But never did he think his wish could come true. Suddenly, Yukio is going to be a big bro?! What a surprise! What a gift! What a... complete NIGHTMARE! When he dreamt of having a brother, being groped and defiled was not a part of the plan. Now, not only does Yukio have to accept his father's secret lover as his new dad, he must accept his perverted son Masumi as his new brother! All under the same roof!

(Source: Futekiya)

Note: Includes four extra chapters.