Myths and Legends are something that all people of all cultures share. The details may differ but the heroes are adequately heroic regardless of where they originated. So when you are telling a story, a princess is still a princess and a hero is still a hero regardless of where you got the story from. You may have to alter details to suit your needs, but with myth fair use is probably not an issue because most myths are older than any copyright law. There are also a wealth of resources available.
I encourage you to pull from myth when you are looking for material.
Rather than merely telling you to do this, I want to give you a rich piece and some ideas how to adapt it to your story.
The image itself is compelling enough to inspire stories, but the story behind it is just as rich. From the British Museum we have this synopsis:
Princess Takiyasha was the daughter of the provincial warlord Taira no Masakado who tried to set up an ‘Eastern Court’ in Shimōsa Province in competition with the emperor in Kyoto. However, his rebellion was put down in AD 939 and Masakado was killed. After his death, Princess Takiyasha continued living in the ruined palace of Sōma.
This print shows the episode from the legend when the emperor’s official, ōya no Mitsukuni, comes to search for surviving conspirators. The princess is reciting a spell written on a handscroll. She summons up a giant skeleton which comes rearing out of a terrifying black void, crashing its way through the tattered palace blinds with its bony fingers to menace Mitsukuni and his companion.
British Museum Website
If we were to strip the details and leave the core elements, we have a failed rebellion, a ruined palace, an estranged noblewoman(who is also a witch), a hero (who is an official of the government), a companion, and a terrible monster. Extracting these core elements is the key to re-purposing the myth to fit into your story. Merely reshape the core elements using details and flavor as befit your setting.
In a typical western fantasy setting, this is a fairly straightforward affair. “A duke’s failed attempt to carve out his own Kingdom from the eastern provinces leaves the tatters of a rebellion festering upon the eastern provinces. Our heroes are sent by the King to investigate the situation and extinguish any smoldering elements. The investigation leads them to the former Duke’s ruined castle. It seems as if the Duke’s fallen vassals continue to serve him in undeath. The duke’s daughter is actually an accomplished necromancer that is reforming the rebellion with her Father’s living and unliving vassals. The heroes intervene and confront the duke’s daughter, the necromancer, wherein she summons a giant, soul-eating skeleton to prevent the heroes from interfering any further in her plans.”
This story can even fit in a 1920’s horror setting! “An eccentric millionaire dies in an armed protest of the income tax. After the uproar dies down and the issue is sufficiently swept under a rug, a squad of G-men are sent to investigate and assess the status of the deceased millionaire’s estate. The estate is expansive and largely derelict. The G-men find a few people remaining at the estate, but they all seem a bit unusual. The young daughter of the deceased millionaire is discovered inside the mansion, frail and harried. She turns out to not be as helpless and meek as she first appeared, as she is possessed by a demon who holds sway over the deceased millionaire’s cursed wealth and fortune. The possessed girl summons unholy monstrosities from beyond the grave to dissuade the G-men from continuing, or even leaving for that matter.”
Both examples share the same base elements, however, they are both quite different in style and detail. I am sure you could conjure up a few more story ideas using a different setting or theme. With a bit of practice, even myths well-known by your players could be adapted without them even realizing where the story came from. Real myths and legends could even become the myths and legends of your world.