World Trigger: Season 2

Season overview

Topic: World Trigger Season 2.
Constraint 1: Use ONLY provided SYNOPSIS and SOURCES.
Constraint 2: Output format: JSON object only.
Constraint 3: Keys: overview (160-220 words) and primer (array of exactly 4 concise bullet points).
Constraint 4: Style: Neutral, encyclopedic prose, plain text, no markdown, no asterisks, no headings, no bullet points in the text.
Constraint 5: No inventing/guessing. If not in material, omit.
Synopsis: Border defense organization "Border" fights "Neighbors" with unknown power. Osamu Mikumo (Border member) forms Mikumo Squad with Yuma Kuga (Neighbor met by chance) and Chika Ametori (childhood friend). They struggle to win internal Border rankings to join the expeditionary force to the Neighborhood.
Source 1: Gate to another world opens in Mikado City, monsters called Neighbors emerge.
Source 2: Earth's weapons do not affect Neighbors. A mysterious group of warriors fights them. Cast: Yûki Kaji, Tomo Muranaka, Brian Doe Chua, Nao Tamura.
Source 3: Gate in Mikado City. Osamu Mikumo is a Border Defense agent.
Source 4: Nao Tamura voices Chika Amatori.
Note on Season 2: The provided text does not explicitly mention "Season 2" narrative arcs. It describes the general premise of the series. However, the prompt asks for a summary of "this season's narrative arc" based only on the provided material. Since the provided material describes the core premise (Osamu, Yuma, Chika, Border, Neighbors, ranking to join expeditionary force), I must use that information. I cannot invent Season 2 specific plot points if they aren't in the text. The text describes the struggle to win rankings to join the expeditionary force.
Drafting Overview (Goal: 160-220 words):
The series follows the events surrounding the emergence of monsters known as Neighbors, which appear through a gate to another world that opened in Mikado City. Because Earth's weapons are ineffective against these entities, a mysterious group of warriors and the Border defense organization were established to combat the threat. Osamu Mikumo, a Border Defense agent, forms the Mikumo Squad to navigate the challenges presented by these attacks. His squad includes Yuma Kuga, a Neighbor whom he met by chance, and his childhood friend Chika Ametori. The narrative focuses on the squad's