Gender change and marriage. The System barely ever shows up, so strictly speaking, this probably isn't a System novel.
Programmer Su Lin died from overwork and woke up as the daughter of a marquis in an otome game.
The System coldly displayed her mission: win over five male leads and achieve the perfect ending, or have her soul trapped in another world forever.
“Win them over? I'm a man.”
She wanted to give up and do nothing. But doing nothing would get her killed.
The stoic knight pinned her against the wall, his voice low. “I'll protect you with my life.” The gentle upperclassman lifted her wrist in the library, pointing out that her palm was the wrong size. The scheming information broker cornered her by a bookshelf and leaned close to her ear. “You're lying.” The tsundere elf handed her an umbrella in the rain and turned away, saying it was no big deal.
Then there was the blond swordsman. He held her hand from behind and taught her to swing a sword, the warmth of his palm searing into the back of her hand. “Will you come back tomorrow?”
She wanted to say no. But why did it feel like these people were trying to win her over instead?!
It's a pure literary work, even the heroine doesn't close the door when changing clothes.