Shun Midorikawa is a member of Kusakabe Unit. Yoneya likened Midorikawa's personality to a "puppy dying to show off its talents". This was shown when he humiliated Osamu by defeating him effortlessly ten times in front of a large crowd. However, in front of Jin, he acted very silly and energetic, because Jin saved Midorikawa in the past.
(Source: World Trigger Wikia)


One day, a gate to another world suddenly opens in Mikado City. Aliens invincible to Earth’s weapons, called “Neighbors”, start coming over. Earth’s only line of defense is a mysterious group called the “Border” who are armed with weapons called “Triggers”. 
 
Four years later, the city has recovered from initial attacks and citizens of Mikado City have started to get used to the Neighbor’s attacks. Yuma Kuga, a transfer student, and his classmate Osamu Mikumo find themselves fighting a Neighbor that suddenly appears. Osamu, who is actually a Border agent, activates his Trigger but is unable to defeat it. This leaves Yuma to activate his own Trigger and defeat the alien. Yuma reveals that he is not part of Border and is actually a Neighbor who has transferred from the other side. 
 
(Source: Crunchyroll)

A gate to another dimension has burst open, and from it emerge gigantic invincible creatures that threaten all of humanity. Earth's only defense is a mysterious group of warriors who have co-opted the alien technology in order to fight back! 
(Source: Viz Media)

The second season of World Trigger. 
 
The border defense organization "Border" was established to fight against the attacks of the "Neighbors" who possess unknown power. 
Osamu Mikumo, a member of the Border, forms the Mikumo Squad with Yuma Kuga, a Neighbor who he met by chance, and his childhood friend Chika Ametori, and they struggle to win the internal Border rankings in order to join the expeditionary force to the Neighborhood. 
 
(Source: Toei Animation)