Context: Akaza Akari 赤座あかり, a 13 years old girl, regrets not being 14 years old like her friends, because they started middle school one year before her, so she spent a whole year without going to school with them.
Akari ga {mou ichinen hayaku} umaretetara dougakunen datta noni あかりがもう一年早く生まれてたら同学生だったのに If Akari had been born {one year sooner} [we] would have been in the same year of school. (counterfactual conditional.)