Ordinary boy Sherlock Doyle finds that his genius sister Glinda has abandoned her post as a royal tutor and that unless he takes her place, they could both be executed. He finds himself having to teach maths to the king's five young children, while attempting to stop anybody finding about his true gender.
I'm a Royal Tutor in My Sister's Dress provides examples of:
- The Ace: Glinda is a prodigy who graduated from college at a very young age and was hired as a royal tutor at only seventeen years old.
- Accidental Pervert: Sherlock, in his hasty attempt to leave the castle, accidentally sees Ryuuju bathing. Then he proceeds to fall into Seira's bath.
- Adaptation Expansion: The original manga only ran for two volumes from June 2011 to July 2012. The Light Novels ran for eight volumes from 2012 to 2015.
- Age-Gap Romance: Sherlock and Seira are eight years apart, with Sherlock being 17 and Seira only 9 when they first meet. Seira later develops a crush on Sherlock after discovering his true gender. They end up together at the end of the light novels, after several years of Seira trying to court Sherlock.
- Always Identical Twins: The princesses Sarasa and Orie are identical twins.
- Attractive Bent-Gender: Sherlock looks really pretty in a dress, which is why he can pose as his own sister. As "Glinda", Sherlock has amassed a large amount of male admirers, much to his dismay.
- The Beautiful Elite: Sherlock is shocked at how beautiful everyone in the royal family is.
- Child Prodigy: Seira, whose intelligence is said to be on par with Glinda's.
- Comedic Spanking: Sherlock spanks Sarasa and Orie after he finds out the twins lied to him about their mother being dead. He later feels mortified by his own actions after the newspapers write about it.
- Crush Blush: Ryuuju blushes whenever his Hot Teacher "Glinda", unaware that he's actually crushing on the real Glinda's twin brother Sherlock.
- Disguised in Drag: Sherlock is forced to disguise himself as his own twin sister to take up her job as a royal tutor, much to his dismay.
- Dude Looks Like a Lady: Sherlock looks so girly that he just needs to put on a dress to pretend to be his sister without anyone suspecting anything.
- Emotionless Boy: Shin doesn't any emotion and has yet to speak.
- Girlish Pigtails: The young princesses Sarasa and Orie style their hair in twintails.
- Godiva Hair: Seira's long hair covers her chest when Sherlock accidentally falls into her bath.
- Grade Skipper: Glinda is such a genius that she got into college when she was seven.
- Hair of Gold, Heart of Gold: Sherlock is blond and a textbook Nice Guy.
- Half-Identical Twins: Sherlock and Glinda are fraternal twins, but they look so alike that Sherlock can pass off as Glinda when wearing a dress.
- Improbable Age: Glinda got a professor degree when she was only twelve years old.
- Intelligence Equals Isolation: Because of her intellect, Glinda never played with other kids besides Sherlock.
- King Incognito: Queen Yuki dresses as a maid on occasion, which is why Sherlock didn't realize her true identity at first.
- Long-Haired Pretty Boy: Sherlock is a cute boy with long blond hair, which helps in his disguise as his sister.
- Massive Numbered Siblings: Ehren's royal family has six children: Ryuuju, Seira, Sarasa, Orie, Shin, and Suzuna.
- Meido: Anneth is a maid working at the royal palace.
- Mom Looks Like a Sister: King Cecillo looks like an older brother to his children rather than a father.
- Named After Someone Famous: Sherlock is quite obviously named after the famous fictional detective Sherlock Holmes. The last name that he and his sister share is taken from Sherlock Holmes's author, Sir Arthur Conan Doyle. His sister Glinda is named after the Sorceress in the Land of Oz.
- Nosebleed: Ryuuju gets one after Sherlock's shirt accidentally falls off, thinking that Glinda's breasts had been exposed.
- One Cast Member per Cover: Most of the light novel's volumes have a different character on each cover.
- Precocious Crush: The 11-year-old Ryuuju develops a crush on the 17-year-old Glinda who, unbeknownst to him, is actually Sherlock.
- Private Tutor: Glinda was originally planned to be this before her disappearance and her place was secretly taken by her brother Sherlock.
- Reports of My Death Were Greatly Exaggerated: Sarasa and Orie tell Sherlock that their mother is dead and their father is only deluding himself into thinking she's recovering from the birth of their youngest child. Turns out the queen is alive and the twins were just messing with Sherlock.
- Sibling Triangle: The first prince Ryuuju and the first princess Seira both develop a crush on Sherlock. Ryuuju thinks Sherlock is a woman because of his disguise, but Seira finds out he's a guy early on.
- Sugar-and-Ice Personality: Seira is very stoic and reserved, but still a sweet girl.
- Teacher/Student Romance: Both Ryuuju and Seira develop a crush on Sherlock after he becomes their royal tutor. Sherlock ends up with Seira at the end of the light novels.
- Teen Genius: Glinda is already considered an outstanding genius at the age of seventeen.
- Theme Twin Naming: The twin sisters Sarasa and Orie are both named after textile fabrics.
- Trickster Twins: The twins Sarasa and Orie enjoy messing around with Sherlock.
- Tsundere: Ryuuju is very gruff towards "Glinda" despite obviously having a crush on his pretty tutor.
- Twin Switch: The premise is about Sherlock needing to disguise himself as his own missing twin sister Glinda and take her place as a royal tutor.
- What If?: One side story about what'd happen if Sherlock wasn't an example of Dude Looks Like a Lady. He expected it'd make Helmut give up the plan to pass him up as Glinda but to no avail. He was deemed a masculine girl and the only girls he attracted were masculine as well. He was glad it was All Just a Dream.
- Wise Beyond Their Years: Seira is very sensible and smart for a 9-year-old.
- Yaoi Fangirl: Anneth, who ships her king and Halmut together.