Complex sentence: During the period of Haruka's bondage to Kantarou, Haruka loses a significant amount of his power, is unable to recall who sealed him in the first place, and is unable to eat oni.
Split into simpler sentences: During the period of Haruka's bondage to Kantarou, Haruka loses a significant amount of his power. He is unable to recall who sealed him in the first place, and is also unable to eat oni.