import re
query = "ABCDE"
full_text = "%EFGHI\r>XXXXX\r>XXXXX\r%IWANT\r>XXXXX\r>ABCDE"
print(re.search("%([^\r]*)(?=(?:\r(?!%)[^\r]*)*\r>[^\r]*{})".format(query), full_text).group(1))
aW1wb3J0IHJlCnF1ZXJ5ID0gIkFCQ0RFIgpmdWxsX3RleHQgPSAiJUVGR0hJXHI+WFhYWFhccj5YWFhYWFxyJUlXQU5UXHI+WFhYWFhccj5BQkNERSIKcHJpbnQocmUuc2VhcmNoKCIlKFteXHJdKikoPz0oPzpccig/ISUpW15ccl0qKSpccj5bXlxyXSp7fSkiLmZvcm1hdChxdWVyeSksIGZ1bGxfdGV4dCkuZ3JvdXAoMSkpCg==