If you're looking for manga similar to My Sister, My Writer, you might like these titles.
Writing light novels isn't all that easy, especially when you're in high school...and you have to do the cooking and the chores for your shut-in stepsister who's hardly come out of her room the past year! In the light novel business, it's crucial to have the right person illustrating your books to help them sell--and maybe get made into manga and anime! But in a world of online pen names, the author and the illustrator may still not even know each other...until one day they realize they've been living in the same house all along!
The "new sibling romantic comedy" revolves around Masamune Izumi, a light novel author in high school. Masamune's little sister is Sagiri, a shut-in girl who hasn't left her room for an entire year. She even forces her brother to make and bring her meals when she stomps the floor. Masamune wants his sister to leave her room, because the two of them are each other's only family.
Itsuki Hashima is a novelist who's hopelessly enamored with the idea of little sisters and is constantly surrounded by colorful characters. A world class genius and love-guru who's beauty almost seems a waste on her. A girl who's constantly troubled by her friendships, love interests, and can't even find refuge in her dreams. A ridiculously talented illustrator. Each of them have as many problems and worries as the next and they never have a dull day together as they play games, travel, and work together.