In the anime and manga series "Blue Exorcist" created by Kazue Kato, there are several characters with exceptional abilities and power. The strength of characters can vary depending on the context and storyline of the series, and power levels may change as the story progresses. Here are some notable characters known for their strength in "Blue Exorcist":

1. Rin Okumura: The protagonist of the series, Rin possesses immense demonic power as he is the son of Satan. He has extraordinary physical abilities and can wield the destructive flames of his demonic heritage. As the series progresses, Rin continues to grow in power and develop his skills.
2. Mephisto Pheles: Mephisto is one of the main characters and the chairman of True Cross Academy. He is an extremely powerful demon with a mysterious agenda. While his true power and capabilities are often kept hidden, he displays a wide range of magical abilities and knowledge.
3. Shura Kirigakure: Shura is an upper-rank exorcist and a mentor to Rin and his classmates. She is highly skilled in swordsmanship and possesses powerful demonic flames. Shura's combat abilities and experience make her a formidable opponent.
4. Yukio Okumura: Rin's twin brother, Yukio, is a prodigy exorcist with exceptional intellect and skill. He is known for his marksmanship and tactical abilities, as well as his use of various weapons and exorcist techniques.
5. Arthur A. Angel: Arthur is a fellow student at True Cross Academy and a skilled exorcist. He wields a sacred sword and is known for his swordsmanship and magical abilities.

It's important to note that the power levels and rankings in "Blue Exorcist" can be subjective and may change as the series progresses or new characters are introduced. The strength and abilities of characters can also depend on various factors, including their training, experience, and the specific circumstances of the story.