Honestly one of the, if not the best shounen manga you could read. The power system it by far the best I've seen besides Nen and the story itself is also amazing. Ashihara does a great job developing the side characters and you really care for them. Each character is pretty unique as well so it's an even better job well done. I do recommend you to read it, and to go all the way through since the beginning is kinda slow. Osamu is a great MC in how he isn't super overpowered and doesn't randomly get overpowered throughout the story. Yuma is the stronger MC and is super experienced. He lives in an almost dead body so it really gives a good plot driver. Chika is by far the MOST OP character in the series, but she is still lovable as she learn to get used to using her power. Jin is the less prominent MC but he still is considered one. He is vital to Border's success and is a great Senpai to the other 3 and gives them many opportunities to survive on their own. There are also many side characters. For example there is Wakamura who is Osamu except even less talented and is in a team with a leader who doesn't listen to others's(she gets better later on too). There's also the characters at Tamakoma branch such as Yotaro and Raijinmaru. They are the comedic value of the series but they are also important to the plot (I can't explain because spoilers). Konami, Reiji, and Torimaru are there to guide the 3 MCs in their journey to go to the neighborhood (the alternate dimension that neighbors live in). In this action and story filled Shounen you will get your fair share of uniqueness and will leave with a connection to the characters.
In Mikado City Humans are overwhelmed at first when their weapons are found to be useless against Neighbors, until a mysterious organization appears that is able to repel the Neighbors' attacks. The organization is called the National Defence Agency, or "Border," and has appropriated the Neighbor technology called "Triggers," which allows the user to channel an internal energy called Trion and use it as a weapon or for other purposes. By activating a trigger, the body of users is replaced by a battle-body made of trion which is stronger and more resistant. Members of Border are divided in three ranks, A, B, and C, with only the members of rank A possessing the most powerful triggers, comparable in strength to those of Neighbors.

Four years later Mikado City has gotten used with the occasional battles with the Neighbors and have returned more or less to their everyday lives. The story follows a Yuma Kuga who transfers to Third Mikado City Middle School where he meets another boy named who is a Border Agent. However, it turns out that Yuma is actually a Humanoid Neighbor, and his arrival signifies that not all is what it seems in the war against the Neighbors.