When Rakuten launched a mobile service network in Japan in 2020, the e-commerce and fintech giant promised to disrupt the world's third-largest telecoms market. It's done that in part, but the greater shake-up has been to its finances.

By any measure, cash-bleeding Rakuten Mobile is deeply troubled.

Founder and CEO Hiroshi "Mickey" Mikitani's initial vision of a low-cost network using cloud-based software and cheap hardware did not pan out as infrastructure costs spiraled. A too-quick rollout earned Rakuten a reputation for spotty coverage it is still trying to repair.