The main character is insanely strong and has a spirit sleeping inside him. He can use all kinds of magic because he trained under some elves, and he goes on a long journey to see the world because he got isekai'd into the world(?)
After some time and meeting many different companions. The (female) spirit awakens, and he goes back home, where it turns out she is the strongest spirit ever because she can use all kinds of magic after the spirit from a great tree inspects her.
This is Seirei Gensouki: Spirit Chronicles.
Haruto Amakawa is a Japanese college student who died in a train crash before he could reunite with his childhood friend, Miharu Ayase, whom he hadn't seen in five years. Next thing he knew his memories resurrected in the body of a boy, Rio, living in the slums of the Bertram Kingdom in the Stralh region of another world. Two people with entirely different backgrounds and values—Rio wants revenge on behalf of his mother, who was murdered in front of him. Complicating matters, Rio suddenly encounters a kidnapping involving the two princesses. After Rio is cleared of abduction, the royalist rewards him with acceptance to the kingdom's academy for studying magic and swordsmanship. However, Rio is shunned by most of the peers there due to being a peasant. His only companion there is Celia Claire, a young female teacher who invites him into her laboratory on a daily basis. Before graduating from the academy, due to a false accusation, Rio became a fugitive and was forced to flee the country. He promises Celia that he will return once he travels to the far east of his mother's homeland to find his roots and stabilize his mixed personality. Along with Haruto's memories, Rio awakens a "special power," and it seems that if he uses it well, he can live a better life.
One of the characters is a "high class spirit" that sleeps within the main character for most of the first couple of serials.
Aishia is Rio's contracted spirit. She is willing to do anything for the sake of Haruto's happiness. Rio learned that she is an upper high-class spirit after he met the Spirit of the giant tree, Dryas.
