Red Sun Rising Order of Battle - Nerima Division, Japan
Japan 1st Division "Nerima" (Mechanized)
In an alternative timeline, with support of the good ole' USA and more than less consent from its neighbor South Korea in response of the rise of PR Chinese military power, in 2001, Japan revised it's constitution, especially the article 9, and transformed the JSDF into a full fledged armed forces under the name "Imperial Defense Forces" (JIDF). The name "Imperial" was chosen due to the Emperor had been once more got designated as de jure Commander in Chief, although largely ceremonial akin to British Monarchs.
The following unit here, the 1st Division "Nerima" is a motorized area security division (Regional Deployment Division in JGSDF parlance) in real life, but in this timeline as part of the new JIGDF (Imperial Ground Defense Force), it's role is a heavy mechanized division, similar with it's South Korean counterpart the "Capital Mechanized Infantry Division"
Primarily equipped with home-grown systems such as tracked Type 89 IFV, Type 90 RCV (fictionalized version of Type 89 but for recon, kinda like M3 Bradley) and newer Type 22 IFV, as well as Type 10 tanks, Type 96 Middle-Range MPM, Type 93 Closed Arrow, Type 87 SPAAA, Type 11 Tan-SAM Kai II, and Type 99 Self-Propelled Howitzers, as well as license-produced systems as following:
Chunmoo MLRS (as Type 22)
Milrem-licensed ground combat drones
Unmanned Little Bird (as H-6JU)
Notable imported equipment included US-made HIMARS, an interim solution prior to the arrival of the Type 22 MLRS but still in use when WW III broke out in the spirit of interoperability within allies.
Rounding up the division are various support vehicles including home-grown directed energy weapon systems as well as swarming UAVs.
The 1st Division is also the only IGDF division with two heavy mechanized brigades in lieu of mix of mechanized and rapid deployment brigades.
Like in real life, the Nerima Division is responsible for defense of Tokyo Metropolitan Area, Chiba, Ibaraki, Kanagawa, Saitama, Shizuoka and Yamanashi prefectures, and in this timeline, due to it's capability it's strongly geared for counterattack mission alongside and in support of wheeled Medium Divisions and Brigades (Rapid Deployment), in which they executed in 2025 when World War III in the Pacific broke out and the subsequent PR China attempt to invade Japanese islands.
Your Lie in April main hero Arima Kousei served as tank platoon leader in the 11th Tank Regiment of the division, while his lover Kaori covered him as a mechanized infantry officer.