Four Leaf Clover
In the year 2015, a signal was broadcasted from space, said to be sent from an Extraterrestrial life form. Soon in 2019, a large number of people have gone missing overnight without any explanation. Many people suspected it to be aliens, the government refutes all those claims, saying that these disappearances are somehow connected to a Trafficking ring, but the people knew better.
Now in 2315, The world is now at war with the extraterrestrial life, 'The Homines' are what they're called. The U.S. Government has launched a space program where they will train child soldiers into combat so that they can face these aliens and all other threats to the Human Race.
(Though you would still understand the plot without reading ‘Follow the North Star’, there will be some elements and character carried over from the first part, therefore I recommend reading that first)