google translated, allegedly 20 additional Jap comps included in the list
google translated so translation maybe not direct
1. 防衛研究所（National Institute for Defense Studies）
2. 陸上装備研究所（Ground Systems Research Center）
3. 艦艇装備研究所（Naval Systems Research Center）
4. 航空装備研究所（Air Systems Research Center）
For entity 1-4, these are Japanese government R&D brain; these are the state bodies that design, prototype, and test essentially every indigenous Japanese main battle weapon system such as tanks, ships, sonar, missiles, aircraft. Listing them constrains the upstream of future domestic development directly. This cluster is comparable to DARPA of DoW.
5. 日鋼特機株式会社（NIKKO TOKKI Co., Ltd.）
6. 日鋼YPK商事株式会社（NIKKO-YPK SHOJI Co., Ltd.）
For entity 5-6, these two are the sole domestic maker of large-caliber gun barrels and missile launcher platform for tank, naval, and artillery large caliber guns like Type-19 self propelled howitzer, 5-inch maritime gun and various missile launchers. This cluster mainly focus on the raw material and machine tools supplies for JSDF.
7. 三菱電機ディフェンス＆スペーステクノロジーズ株式会社（Mitsubishi Electric Defense and Space Technologies Corporation）
8. 三菱電機ソフトウェア株式会社（Mitsubishi Electric Software Corporation）
9. 三菱電機エンジニアリング株式会社（Mitsubishi Electric Engineering Company, Limited）
10. 三菱プレシジョン株式会社（Mitsubishi Precision Company, Limited）
For entity 7-10, these are Mitsubishi Electrics' subsidiaries:
These are the core suppliers of Japanese AESA radar, missile seekers and guidance computers, satellites, and electronic warfare specific equipments. Especially 三菱プレシジョン (Mitsubishi Precision) makes gyroscopes, inertial navigation, fuzes, guidance components, and training simulators. This cluster is the sensing-and-guidance layer of JSDF.
11. エムエイチアイオーシャニクス株式会社（MHI Oceanincs Co., Ltd.）
12. MHIさがみハイテック株式会社（MHI Sagami High-tech, Ltd.）
13. 株式会社エムエイチアイロジテック（MHI Logitec Co., Ltd.）
14. 光和興業株式会社 (KOWA KOGYO, Ltd.)
15. 菱重特殊車両サービス株式会社（MHI Special Vehicles Parts Supply & Technical Service Co., Ltd.）
16. MHIマリテック株式会社（MHI Maritech, Co., Ltd.）
For entity 11-16, these are Mitsubishi Heavy Industries(MHI)'s subsidiaries:
MHI builds Japan's destroyers, submarines, missiles, and tanks. The listed subsidiaries are its support and subsystem ecosystem: MHI Oceanics makes undersea, both AIP manned subs and UUV systems, MHI Sagami High-tech makes precision components for missiles and sats, MHI Logitec is the main contractor for strategic defense logistics. MHI Special Vehicles supplies parts and technical service for combat vehicles such as Type 10 and Type 90 tanks as well as armored vehicles. MHI Maritech (marine technology/ship support). This cluster is the JSDF platform-and-sustainment layer.
17. 株式会社ケージーエム（Kawajyu Gifu Manufacturing Co., Ltd.）
18. 日本飛行機株式会社（NIPPI Corporation）
Entity 17 and 18 belongs to the Kawasaki Heavy Industries(KHI) cluster which is the aerospace manufacturing arm: these are the main supplier of P-1 patrol aircraft, C-2 transporter, and BK117 helicopters. NIPPI is 100% owned by KHI.
19. フォルトゥニオ株式会社（Fortunio Co., Ltd.）
This company provides counter UAV warfare solutions.
20. 青木精密工業株式会社（Aoki Seimitsu Kogyo Co., Ltd.）
This company provides precision gears and gearboxs.
This list accuratly hits most of the top-tier Japanese defense contractors.
