#War/s

Never having known the warmth of family, he was reborn in another world. Named Yuri, he is doted on by his parents and lives a new life in peace – as it should be. However, the country where Yuri and the others live is threatened by the “other humans” who dominate the vast expanse of the continent and is in danger of dying. Yuri and his family can’t stay out of it and are caught in the middle of the war… The Knights' House, the sword of the kingdom that wields a lance and kakedori birds. The death of his uncle, who was the leader of the Hovu family, brings Yuri’s father back to the world of knights, who had left the house to hate killing each other. Yuri is forced to attend the Knights’ Academy, where knights are trained, and the encounter there will drastically change the fate of Yuri and the kingdom. This is the story of a man who fights for the people he loves and later became known throughout the world as the “Demon King.”
 
As a self-professed no-lifer, Yuri idles his days away in front of a computer. This all changes the moment his life in Japan comes to an abrupt end and he finds himself reborn in the strange new world of the Shiyalta Kingdom. His new life includes everything he once lacked: loving parents, a comfortable home, and a promising future breeding and raising birds on his dad’s ranch. For centuries, the kingdom he now calls home has enjoyed peace and prosperity, shielded by friendly nations that, like Shiyalta itself, were established with the collapse of a once-great empire. War is a distant problem, relevant only to Shiyalta’s ruling families whose warriors periodically set out to join the fighting upon massive birds trained by Yuri’s dad and others. But this peaceful existence can’t last forever. Something rotten lies at the heart of the kingdom, and it doesn’t take someone with Yuri’s exceptional intelligence to realize that those distant battles will only remain irrelevant for so long.

Deep in Scotland Yard in London sits an evidence room, where artifacts of the greatest mysteries in London history are kept. In this "Black Museum" sits two bullets, fused together after a head-on collision. This was the key piece of evidence in a case that brought together a supernatural Man in Gray and the famous nurse and activist Florence Nightingale—the only person who can see him. Surrounded by war and suffering, the lady enters into a desperate pact with this ghostlike man…
 

In a world where humans sell and buy otherworldly species as slaves, the great mage Rifenhardt is treated like the Demon King for helping the otherworldly species.
A party of heroes arrive to bring down the Demon King! Rifenhardt succeeds in greatly injuring the heroes, but he faces death at the hands of... the Martial King Tesslon!
"Time and Space Regression Spell."
However, Rifenhardt miraculously manages to cast this last-resort spell and regresses to the past. But...
“Who are you?”
He awakens reincarnated in the body of the continent’s strongest physical warrior, Tesslon!
Now begins Rifenhardt's adventures as both a great mage and the physically strongest man to change the world!