Question: who sings the opening song for blue exorcist
[{'answer': 'Uverworld', 'provenance': [{'wikipedia_id': '24327353', 'title': 'Blue Exorcist', 'start_paragraph_id': 20, 'start_character': 82, 'end_paragraph_id': 20, 'end_character': 91, 'bleu_score': 1.0, 'section': 'Section::::Media.:Anime.\n'}]}, {'provenance': [{'wikipedia_id': '24327353', 'title': 'Blue Exorcist', 'start_paragraph_id': 22, 'start_character': 0, 'end_paragraph_id': 22, 'end_character': 525, 'bleu_score': 0.808393298125835, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1508588655993556029}, 'section': 'Section::::Media.:Anime.\n'}]}]