Hidden Identity

Prophecy / secret cross dressing

Princess of eliminated royal family

Man for hire / mission

Secret cross-dressing / crown prince

Time travel (and crosses paths with alternate timeline past version of himself)

Online gaming persona

Tomboy / mistaken gender

Secret cross dressing

School vigilante

FL takes her twin brother's place as crown prince.

Sniper / Righteous Army rebel

The FL hides her background as a rich and beautiful heiress in order to escape her grandfather's control while she searches for answers about her father's whereabouts. 

The ML hides his true identity (crown prince / heir to the emperor of the 5 kingdoms); also the FL is not aware of her true identity

Twins switch places

FL dresses as a boy to attend an all boys military academy.

Robot

The FL hides her true name and status + lives as a commoner under a new name and hides the fact that she is literate; the ML has amnesia and forgets that he is the crown prince; when he realizes he must have been a noble before he lost his memory, he decides to hide his literacy so he can continue living under his new identity. 

Cross dressing / time traveler

Love experiment participant

Energy vampire

Secret cross dressing / god in mortal world / memory loss

Immortal goblin / grim reaper / god

FL covers for / pretends to be her twin; undercover cop pretends to be a wannabe gangster

Secret cross dressing

Secret cross dressing

Immortal alien

Revenge mission

The ML pretends to be the FL's long lost brother in order to get a portion of her inheritance to pay off his debts

Emperor / commoner

ML covers for / pretends to be his older brother

Time travel / secret mission

The ML initially hides his identity as the millennium dragon from the FL.