I Thot You Was a Toad's manga / #dubcon(2)

Abusive relationship between an older male teacher and an underaged male high school student incorporating dubcon, exhibitionism/public sex, secret vibrators, sounding, blackmail and humiliation.

What appears to be a standard half-brother x half-brother incest story acquires suspense when it looks like Masayuki, the heir to his father's company, is being deliberately targeted and sabotaged.