Isekai no Seikishi Monogatari

Kenshi Masaki is a 15 year old boy that unwillingly traveled from his home on Earth to the alternate world of Geminar. In Geminar, the countries wage wars using Seikijin, humanoid weapons that were originally discovered within ancient ruins. After being tricked by a mysterious organization into participating in an attempt to assassinate Lashara Earth , the young princess of the Shitoreiyu Empire, he ends up captured after he chooses not to kill her. When Lashara hears the truth, she decides to help.Disguised as her servant, Kenshi moves with her to the Holy Land, a virtually impregnable fortress that serves as an academy to train Seikijin pilots. With his kindness, tenacity, and skills that vary from carpenting to advanced techniques of survival, Kenshi eventually becomes a celebrity in the academy, becoming the object of affection of many female students and making some of the male students envious. However, the same organization who deceived Kenshi is secretly working inside the academy, and a worldwide conflict is about to begin.

Countries
Shitoreiyu Empire
The home country of Lashara and Chiaia prior to moving to the Holy Land. Shitoreiyu lacks some technological advances, as quoted by Maria, so it relies on using the technologies of other countries such as Havoniwa. It is also the place where the Seikishin and Doll were unearthed. Shitoreiyu's past ruler was Koyo Earth, Lashara's father, but after the latter died, Lashara became his successor. However, Lashara slowly loses her position of power to Babalun after his promotion to Prime Minister.
Holy Land
An impregnable fortress made in the image of the Choushin goddess. It is also home to Holy Land Academy , a special school where nobles and the wealthy train to become Seikishi. The Holy Land also holds the Holy Tournament , a tournament where Seikishi from all over Geminar compete (Aura once stated that Flora was one of the champions). In the Holy Arena, pillars and Ena's Draft are placed as challenging obstacles for the most skilled Seikishi, though Kenshi is able to maneuver through them with ease. According to Lashara, winning the Holy Tournament is the greatest achievement for a Seikishi. It was later invaded and conquered by Babalun, who was after the Shield of Gaia that was buried underneath and Gaia itself, but was later reconquered following Babalun's defeat.
Havoniwa 
The homeland of Flora, Maria, and Yukine, and is one of the more technologically advanced countries in comparison to the others. In Havoniwa, there is a welcome ceremony in the form of a pillow fight, where the competitors are to pull the sashes off of their opponents' yukata and the last person standing wins. Their main defense is the Meteor Fall  a floating fortress that drops meteor-sized rocks to destroy their invaders. It is stated in the anime that the main city that was destroyed by Dagmyer's forces was actually it's governing area and there was little to no residents in the area so it was a small loss to Havoniwa. It also has an underground city in case their main city is destroyed. Havoniwa's capital was destroyed by Doll, but its people managed to find refuge in the underground city.
Shurifon Kingdom 
The nature-affiliated home of the Dark Elves , who have dark skin, silvery-white hair, and blue eyes much like Aura's. Also like Aura, their personalities shift based on the time of day, which is described by others as their "weak periods". In Shurifon, there is a rare mushroom that can be sold for a huge fortune (Kenshi found four during the series' run) and it is often used as a gourmet ingredient in the royal courts. Also in Shurifon, there is an event called the Pot-Dish Battle, where the contestants find ingredients to make a dish. The winner is determined by a judge and the person with the most delicious dish wins. Shurifon was the first of the countries to be destroyed by Dagmyer's forces. It is later revealed by Naua that Shurifon's people were brought to Geminar by the Senshi Civilization in ancient times to pilot the Seikishin.
Church 
The main overseers of Geminar. They are the remnants of the Senshi civilization and are well-aware of the dangers of Seikijin. They tried to prevent the introduction of Seikijin into the current world but had no choice once the Seikishin was unearthed in the Shitoreiyu Empire. To prevent the occurrence of an arms race of the kind that destroyed the Senshi civilization, the Church decided to allot a fixed number of Seikijin and Seikishi to each country to maintain a balance. The Church was shown to have superior technology, such as teleport-pads, apart from monopolizing the construction and repair of Seikijin.
Senshi 
An ancient civilization on the world of Geminar. The Senshi civilization was world-wide and unified, with individual units such as cities and villages. Naua Furan explains that the Senshi civilization created the Seikijin, not for war, but for sports and other athletic competitions. Eventually, the Seikijin were used for gladiator-like fight events, and the Seikishi became an elite class. Massive technological advancements were made to the Seikijin as people tried to one-up their opponents. As the battles between Seikijin grew more fierce and the number of Seikishi fatalities increased, the expertise and fighting instincts of the Seikishi were downloaded onto crystals (called Core Crystals) and embedded into newer Seikishi to preserve them. Over time, the accumulation of fighting skills and bloodlust in the crystals caused the Seikijin to go on a rampage. These rampaging Seikijin (Holy Machine Men) were labelled as Seikishin (Holy Machine Gods) because of their overwhelming power. The human remnants managed to disable the Seikishin, but were too late to save their civilization, which had split into several groups as the people fled the Seikishin.