It is highly probable that you are looking for a series featuring a sister character with this specific personality type. If you enjoyed the quiet, low-key dynamic implied by "Simple Life with My Unobtrusive Sister," you would likely enjoy series like Kotaro Lives Alone (for the simple life aspect) or The Angel Next Door Spoils Me Rotten (for the character dynamic).
Premise
Spend evenings with Mio chatting, watching anime, and cooking meals. simple life with my unobtrusive sister wiki