Great Tree Eniyunien (エニユニエンの大樹, Eniyunien no Daiki) is the spirit born from the rumors and lore of the "Great Tree of Education" and acts as the spirit school itself.
Eniyunien is a tree so high that there's no end in sight, it breaks through the clouds and looks like it will pierce the heavens. Anos even notes that trunk is probably as wide as Dilhade. Inside of Eniyunien, there are classrooms that he can use to teach his students.
Eniyunien has the voice of a hoarse old man, but very calm and composed. As a teacher, he gets very exited when a student asks a question. However, he is very sensitive about his teaching and got angry after the class criticized his bad drawings. He eventually calms down after Anos correctly guesses his drawings and graduates him instantly, showing a self-serving side despite being an educator.
In the spirit school, they teach about various spirits and their history. There are all kinds of other lessons, but the one that is required is the spirit class. These extra courses include swords, magic, cooking, arithmetic, how to train and raise spirits, how to create spirits, etc.
After hearing that the demons from 2,000 years ago were in the spirit school, Anos and his group head there and meet Eniyunien. He explains how the school works and begins class. To make it easy for them, he gives an assignment about famous spirits and draws three figures to identify. When Lina mutters about the poor quality of the drawings, Eniyunien sees this as an attack to his teaching and gets angry, but calms down after Anos correctly responds.
After class ends, Anos asks to reduce the number of tests he had to take before being able to take the spirit trials, but Eniyunien tells him he can't condense it all into one. However, Anos successfully sways him into doing so by comparing his school to the Demon King Academy, where it would be possible due to the teachers' flexibility.
- Magic Space: Eniyunien seems to be skilled in spatial magic. When class starts and the doorway disappears, he sends the whole classroom into a magical space devoid of anything. There is also a swamp inside Eniyunien that is inhabited by the Long Snake Epiteo, who is said to be long enough to encircle the world 333 times.
- Magic Eyes: Eniyunien has excellent magic eye to detect injustice as a characteristic of the Spirit of Education. Its power increases even more in his body.
- Once inside the Great Tree Eniyunien, you will be automatically enrolled in the spirit school.
- You can't leave until you take the spirit class and graduate. Food, clothing and shelter will be provided for you.
- It is forbidden to use violence to hurt or restrain others. If you disobey this rule, you will be punished by having to walk the full length of the Long Snake Epiteo. This is the current punishment, but it may change from time to time.
- Eniyunien will occasionally ask questions about spirits. If you answer correctly, it will be added to your grades. Besides that, there's also quizzes and trials of the spirits that will be graded as well.
- Students with the best grades will graduate and receive a seal of graduation, allowing them to freely come and go from Aharthern.
- You can still take classes after graduating.
- Eniyunien will judge whether you receive good grades or not based on his long-standing teaching intuition. It is more than simply getting good marks on a test.
- If you get a failing grade, you will be spirited away.
- After a few quizzes, those with the best grades can move on to the trials of the spirits. Students who pass will have an audience with the Spirit King, and if they pass the Spirit King's trial, they will graduate as it is.
- The earliest he had ever graduated someone was 2 weeks and the longest was 50 years. However, Anos manages to beat this record by Day 1 by getting into Eniyunien 's good graces.