Mint Chocolate Vol. 1 (manga)

It's an absolute secret--our relationship!
When Nanami finally gets a chance to meet her mom's new husband and his son, the last person she expects to see is one of her classmates, Kyouhei Suzumura. Not only is her new stepbrother cool and completely unapproachable, but even worse--he's the crazy-hot guy Nanami's been crushing on for months...! Only time will tell how Nanami's unexpectedly forbidden romance will play out...