Hello Summoner and welcome to the Medieval skin line in League of Legends. These skins are unique in that they do not exist in an alternate universe, rather, they are staged in the distant past; the Medieval Age.
In this lore, we get to experience several regions in Runeterra as they were in the past. From ruling houses and rival factions in Freljord to a filthy assassin in Zaun and even a rampaging knight in Noxus. I like this skin line because it covers more regions, unlike other skin lines that are restricted to a region or no region at all.
While we can only guess at the villains in this world, we are sure that the darkness will rise at Freljord. Based on the region, it’s safe to say Lissandra will join this skin line soon. The reason is that her normal bio tells of her desire to encase the world in dark ice, starting from Freljord.
Medieval (Queen Ashe)

Queen Ashe rules over the Freljordian kingdom. However, she still has other rivals to contend with and an evil bent on destroying the world.
Skin Backstory
A radiant queen once venerated as a figure reborn from legend, Ashe rules her people as the visionary leader of two great Freljordian houses. Yet two equally driven rivals oppose her queendom, as a rising darkness threatens to consume them all.
Medieval (White Mage Veigar)

As much as Veigar yearns to do evil with his powers, he always ends up helping the sick and the weak.
Skin Backstory
A master of healing magic residing within an ancient cathedral, Veigar self-identifies as a dastardly archvillain rather than the pious cleric he clearly is. His magic has cured ailments and dispelled curses from across the land, much to his chagrin.
Medieval Twitch

This assassin loves nothing more than to kill or steal. One thing remains a fact; his love for the filth beneath Zaun is second to none.
Skin Backstory
An assassin-for-hire living beneath Dread Fortress Zaun, Twitch is a disgusting malefactor who has tipped every one of his killing implements in moist, toxic garbage. He excitedly awaits each contract, eager to kill, steal, and destroy as much as he can.
Medieval (Sir Kled)

The self-proclaimed knight pursues the reclamation of his ‘lands’. If you disagree, go face him in honorable combat.
Skin Backstory
Sir Prince Chevalier Archduke Lord Double-Earl Kled (or Sir Kled, for short) is a half-mad knight from the aptly named Kingdom of Kled, which contains exactly two subjects: Kled, and his cowardly avian mount, Skarl. Together, the pair ravage the countryside to ‘reclaim’ Kled’s ‘land’, which apparently is… all land, everywhere.
Medieval (King Tryndamere)

King Tryndamere rules the Freljord alongside Queen Ashe. Although he still has a blood debt to pay.
Skin Backstory
A proud king who was once known only as a brutal highland swordsman, Tryndamere rules his people as the martial protector of two great Freljordian houses. Yet every day he resists the pull of an intangible evil at his back, as he has not forgotten a certain blood debt that he vowed to see repaid.
Medieval (Blacksmith Poppy)

Poppy keeps searching for the hero worthy of the Hammer she wields. Little does she know that the Hero is no one else but her.
Skin Backstory
A famously gruff blacksmith working under the tutelage of Sir Ornn of the Freljord, Poppy wields a hammer imbued with powerful magic that she believes is destined for the weapon for an unknown hero. Little does she know the hammer is the weapon, and the hero… is herself.
Medieval (Sorceress Lux)

Even though her people look down on the use of magic, Lux is determined to open their eyes to its positivity and good uses.
Skin Backstory
An aspiring mage from the Demacian Dukedom, Lux has traveled across the land in her quest to lighten the lives of the peasantry with magic. Through her efforts are often met with suspicion at first, tales of her ‘miracles’ are beginning to reach the ruling class of the Dukedom itself…
Medieval (Little Knight Amumu)

This peace-loving knight is a fervent believer that the world will come to rest and nations will co-exist in peace…..one day.
Skin Backstory
A diminutive knight whose heart is brave and true, Sir Amumu of Shurima wants only to see peace reign the land in his lifetime. Considering that he’s an undying, mummified princeling, he’ll probably succeed.
Conclusion
Although the Medieval skin line leaves a lot of space for the plot, the stories show that while the people of this world carry on their normal lives, they are about to enter an age that would either lead to peace or war.
For another unique universe, check out the Mecha skin line.
Thanks for reading.