The 2 seasons are completely different from each other. The one named Da Capo Second Season starts 2 years later after Nemu had left for a university. Now, as for Da Capo 2, according to anime news network is set 53 years after the original Da Capo characters; meaning that the characters in this one are the grand children of those from the first Da Capo.Originally Posted by narutosharingan
And yes, it's a definite must-watch. Completely different stories from each other, however it's pretty cool how the grand kids are similar to their grand parents