I Will Return My New Brother

Marian, who longs to live a normal, quiet life, suddenly finds herself in a state of change. Her mother's remarriage has brought her a new brother, but the problem is... it's a burden!!

"Until the day I die, not a drop of water will touch your hands."
"Why do you promise that?"
"If you have any wishes, just tell me."
"Please don't stay home and meet your friends outside and get to know them better."

Even more, he's considerate of me, who hates to stand out, and he's even willing to spend money to change my fancy carriage into a more modest one.

Is this person crazy? Or are all nobles this crazy?

I thought my mother's remarriage was just her having a new husband, and it had nothing to do with me. But... can I accept my new family?