Question: who sings the theme song for vampire knight
[{'answer': 'On / Off', 'provenance': [{'wikipedia_id': '22110803', 'title': 'On/Off (Japanese band)', 'start_paragraph_id': 3, 'start_character': 0, 'end_paragraph_id': 3, 'end_character': 14, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}, {'provenance': [{'wikipedia_id': '22110803', 'title': 'On/Off (Japanese band)', 'start_paragraph_id': 3, 'start_character': 0, 'end_paragraph_id': 3, 'end_character': 1277, 'bleu_score': 0.7744530118818751, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 9849799772716851747}, 'section': 'Section::::History.\n'}]}]