I'm No Imperialist, Let Me Show You the Sea of Stars

An alternate-world blue planet: Dragon Star.

A genius with a legacy of the oldest medical arts and the most advanced Western medicine, leader of the Hidden Dragon Unit and captain of the Shadow Squad.

When a viral outbreak swept the world, he worked tirelessly, relying on his own skills to save countless lives. Three months later, after successfully developing an antidote, he died of his injuries.

He activated the Legacy System and transmigrated to another world, where he was reborn on Blue Star...

By all rights, with the System in hand, the world should have been his from the start.

But the System was activated with too little energy, so he had to work for it to earn more. He had thirty years to do so, or the System would self-destruct and take him with it.

With no other choice, the protagonist could only work hard to grow stronger and develop his homeland with all his might.

While quietly building up his strength, he unexpectedly discovered that spies from another race were plotting to destroy the entire nation.

And so began a battle to defend the homeland. Fighting against Heaven was endlessly rewarding, and so was fighting against people.

He had an immensely favorable start and was as steady as they come, but after an accident, the protagonist was put into a years-long coma by the schemes of another race, turning what should have been a sweeping victory into a stalemate.

When the protagonist awakens, the entire planet begins to tremble.

All kinds of weapons far beyond their era make their debut, allowing him to dominate this other world.

Then his family background comes to light, a terrifying race appears, and the invasion by three races begins.

The protagonist boards an aerospace carrier and travels across the stars to rescue the alien humans persecuted by the three races...