New World Lovetopia Memento

Once upon a time there was a "great portal" between the other world and the human world, through which various otherworldly creatures came into the human world through the one-way portal. They began to live peacefully with humans. The tribe of angels, unable to return to their original home, keeps searching for a way to open a "return portal," and they find the key is related to a certain young man…? (Source: Tokyo Mangasha, translated)