| CSi Global Alliance, Inc. | Osaka |
| Cside Net | Tokyo |
| CTY Co., Ltd | Tokyo |
| Cube Magic Co., Ltd | Osaka |
| Cube System Co., Ltd | Tokyo |
| Cuorips, Inc. | |
| CureApp Co., Ltd | Tokyo |
| Curvegrid | |
| Custom Media K.K. | |
| CVC Japan Co., Ltd | Tokyo |
| CWORKS Co., Ltd | Tokyo |
| CXDNext Co., Ltd | Tokyo |
| CXR Engineering, Inc. | |
| Cyber Com Co., Ltd | Tokyo |
| Cyber Communications, Inc. | Tokyo |
| Cyber Craftman's Village | Aichi |
| Cyber Defense Institute Co., Ltd | Tokyo |
| Cyber Matrix Co., Ltd | Tokyo |
| Cyber Security Cloud, Inc. | Tokyo |
| Cyber Solutions, Inc. | Tokyo |
| Cyber Square, Inc. | Tokyo |
| Cyber Station | Tokyo |
| Cyber University | |
| Cyber-Scene Co., Ltd | Tokyo |
| CyberAgent Capital, Inc. | Tokyo |
| CyberAgent Ventures, Inc. | Tokyo |
| CYBERDYNE Omni Networks Co., Ltd | Ibaraki |
| Cybernet Co., Ltd | Tokyo |
| Cybernet Systems Co., Ltd | Tokyo |
| Cyberplus Co., Ltd | Tokyo |
| Cybersolution Co., Ltd | Tokyo |
| CyberSolutions Co., Ltd | Tokyo |
| Cybertrust Japan Co., Ltd | Tokyo |
| CyberWorld | Tokyo |
| CYBIRD Co., Ltd | Tokyo |
| Cybozu, Inc. | Tokyo |
| Cygames Co., Ltd | Tokyo |
| CytoPathfinder, Inc. | |
| CyVerse Corporation | |
| D-Style | Niigata |
| D.I. System Co., Ltd | Tokyo |
| D2 Communications | Tokyo |
| D3 Publisher, Inc. | Tokyo |
| D4V | |
| DA Search & Link, Inc. | Tokyo |
| DACS | Tokyo |
| Daejon Institute of Science and Technology | |
| Dai Nippon Printing Co., Ltd | Tokyo |
| Daicel Corporation | Osaka |
| Daicoh Electronics, Inc. | Tokyo |