Complex sentence: Kosaku realizes he has a once-in-a-lifetime opportunity to get to personally know his dream girl and, together with his group of friends, try to find out why she came to the agricultural school and become more than just classmates.
Split into simpler sentences: Kosaku realizes he has a once in a lifetime opportunity to get to personally know his dream girl. With his group of friends, he tries to find out why she came to the agricultural school and become more than just classmates.