[FairyKing]

Live, thread! Live!!!
I had a new idea, inspired mainly by the early "Geats is a viking" rumor and fantasy RPGs:

From the magical world of Runegard, a warrior has come to Earth. His name: Kamen Rider Viktor! But is he here to protect, or to conquer?

Our main rider is Kamen Rider Viktor, AKA Vikor Aegis (nicknamed "Vikkun" by an Earthling friend), an uncouth, hotheaded man who just does whatever he wants, but he has a strong sense of honor and can't stand those who prey on people weaker than themselves. While he does protect people from monsters, at first his main motivation is just the love of a good fight, while the heart of his character development is about learning to care for the people around him and fight for a greater cause.

The second rider is Kamen Rider Sylvan, AKA Sylvan De Rafiliam, a polite, refined but somewhat stuck-up elf lady who wants to live a peaceful life. Unlike Viktor, she doesn't enjoy fighting at all, but reluctantly takes up arms to protect her new home on Earth, and shows she can be a very skilled fighter when needed. However, she doesn't reach true power until she overcomes her hesitation and accepts that in order to protect the peace of others, she must be willing to give up that peace herself and fight with her whole heart.

And the third rider is Kamen Rider Keiji, AKA Saito Keiji, an earnest and hardworking policeman from Earth, who happens to be assigned to the area where Viktor, Sylvan and various other Runegarder immigrants live. At first he has trouble interacting with Runegarders, but as he gets to know them better he becomes their steadfast ally and even stands up for them against his prejudiced higher-ups, culminating in being the first Earthling to transform with Runegardian magic!

There would be more Riders, with varying levels of plot importance, but those three would be the most focused on.

The story is that portals have started opening between Runegard and Earth, seemingly at random, allowing people to pass from one world to the other, though most are unstable and close after a short time. But Runegard, as a world of magic, is also inhabited by monsters, which wreak havoc when they come through a portal to Earth. The first arc is mostly-episodic battles against these monsters, but with some ongoing plots about the Runegarder characters adjusting to life on Earth and the Earthling characters learning more about Runegard.

In the second arc, the intro changes to:
From the magical world of Runegard, an army has come to Earth! Their name: The Jadheim Empire! Will the Kamen Riders side with them, or against them?

The second arc begins when magic scholars of the Jadheim Empire figure out how to make stable portals, and begin sending through lone warriors (other Kamen Riders) or small strike forces (Iron Troopers, Rider-like footsoldiers). At first they claim their goal is to protect Earth from monsters, but Viktor never trusts them, and soon exposes their true goal: Laying the groundwork for an invasion! Once exposed, they drop the pretense and start attacking openly, unleashing captured monsters, along with their more elite warriors... including Viktor's younger brother, Kamen Rider Connor, AKA Prince Connor Aegis Von Jadheim!

And in the third and final arc, the intro changes again:
From the scientific world of Earth, Kamen Rider Viktor has returned to Runegard. His true name: Prince Viktor Aegis Von Jadheim! But will his quest bring freedom, or destruction?

The second arc ended with Viktor and his allies stopping the Jadheim invasion, but in the process getting stranded in Runegard. So in the third arc, they continue their war against the Jadheim Empire while also searching for a way home. During this, the other characters learn the truth of Viktor's past: He was once the crown prince of Jadheim, but despised their oppressive rule and ran away to Earth to live a carefree life. Now home and faced with the responsibilities he'd abandoned, he fights to free Runegard from his own family's tyranny, and eventually he'll have to decide whether to claim the throne for himself, or destroy the Empire entirely...