A Mysterious Boy On The Park

A man who saved his beloved realm from its fate woke up in another world. Clive Rosfield was found in a new world he had never known, the Academy City in Tokyo, Japan, the modern world unlike in the Realm of Valisthea, and reverted him to 15 years old. Clive will find new friends, including familiar ones, and his enemies and discover a strange new realm of supernatural power. But they didn't know the people of Academy City will witness a powerful but terrifying and devastating beast hadn't seen before that is unrelated to the espers...the Eikons.

Disclaimer: I don't own any of these animes and the Final Fantasy XVI, credits belongs to the respective owners.