The Holy Kingdom of Saillune (Japanese: 聖王国セイルーン, Romaji: seioukoku seirūn, also translated as Seyruun by CPM) is perhaps the most influential nation within the mazoku barrier. Residing around the middle of the peninsula, it borders the Alliance of Coastal States and the Kingdom of Ralteague from the west, the Kingdom of Zephilia and Kalmaart from the north, the Elmekian Empire from the east and the Desert of Destruction from the south. Some maps show Saillune possessing a small part of the coastline to the south instead; this is probably incorrect, although the borders of the kingdoms in the peninsula are not precisely assigned. Its capital is Saillune City, a hub for economy, culture, music and learning.
It is unknown how long ago the kingdom was founded, but it is unlikely that it predates the Kōma War, as most human nations were devastated by the conflict. According to Lina Inverse, the capital was founded "ages ago", meaning that Saillune is probably at least a few centuries old.
Saillune City is also known as the Capital of White Magic, with good reason. The city's layout was designed by a trusted advisor of the king, a white sorcerer, to resemble a giant white magic seal, or a hexagram. (In Slayers REVOLUTION and EVOLUTION-R, this was censored for various reasons, and changed into a pentagram, although that is the black magic seal in Slayers.) All other magic types are suppressed within the city, while white magic spells are amplified. This, along with the fact that the hexagram also provides the capital with multiple layers of reinforced walls, makes the city nigh impregnable. In the anime, it is shown that the main thoroughfares of the city are actually upon the walls themselves, as seen on the picture to the right. Surprisingly, despite the the city's overall wealth and prosperity, Saillune also possesses a slum district, with its fair share of bandit gangs and brothels.
In the center of Saillune, surrounded by another set of high walls, lies the Royal Palace and the Temple of Ceifeed, the main shinzoku worshiped in the nation. The temple is at the exact center of the hexagram, amplifying white magic to the point where even a simple Flow Break is sufficient to seriously damage a middle-ranking mazoku. The temple and the palace is surrounded by a large garden.
Saillune's politics and foreign affairs are exclusively oriented towards keeping the peace in the peninsula. While the state does have an army, it is never used for offense, and no sorcerer of the kingdom uses anything other than white magic, at least officially. This, along with the nation's economical and cultural significance makes Saillune the leading nation in the region; for instance, it organized the joint efforts of sending delegations into the outer world in the beginning of Slayers TRY.
Saillune is a monarchy. The current king is the elderly Eldoran Saillune; he has fallen ill however, and is unable to attend to his duties since 1011 AK(?). Since then, his would-be successor, Prince Philionel El Di Saillune more or less runs the country. The order of succession seems to follow the system of equal primogeniture, meaning that the heir to the throne is always the eldest member of the royal family, with no distinction between genders. Prince Philionel, being a self-proclaimed pacifist, wants to continue the nation's peaceful traditions. Not all of his relatives agree with this, however; plotting and assassination attempts serve as a constant reminder of the family feud since decades, with more and more members of the royal family dying. King Eldoran seems to be powerless to resolve the conflict.
Art and culture in Saillune seems to have an Arabic touch, mostly apparent in architecture and clothing, especially among the royalty. Excessive usage of white materials such as marble can be seen on buildings. Other aspects more or less follow the medieval trend, with some anachronistic elements such as restaurants or public libraries thrown in, something which is common throughout the Slayers world.