Mistletoe
Mistletoe is the Tokyo-based family office of serial entrepreneur Taizo Son, the younger brother of SoftBank's Masayoshi Son, backing impact-driven deep-tech founders who tackle global challenges. Its water bets center on decentralized, climate-resilient supply. As of 2026 Mistletoe has backed 2 water companies, at Seed and Series A.
Compiled by Antoine Walter, (don't) Waste Water, from official filings and direct intelligence in Leviathan.
The take
Mistletoe is the personal investment vehicle of Taizo Son, the youngest brother of SoftBank founder Masayoshi Son, who built it in 2013 not as a fund raising other people's money but as a family office spending his own. That structure is the whole point: with no outside limited partners (the backers who normally supply a fund's capital) to answer to, Mistletoe can write patient cheques for founders chasing global problems rather than the next quick exit.
Mistletoe backs impact-driven deep tech across health, food, education and climate, and water turns up inside that climate slice rather than as a standalone thesis. The two water companies (don't) Waste Water tracks share one clear pattern: both make clean water without the pipes. WOTA builds AI-controlled boxes that recycle water on the spot, and Aquaria pulls drinking water straight out of the air, decentralized kit for places a central utility never reached.
Mistletoe is run by Taizo Son with co-founders Atsushi Taira and Hitoshi Miyata, and Son tends to talk about water in plainly human terms. Backing Aquaria, he framed the point as a way to counter the water crisis in Asia and make water accessible to all, rather than as a clever piece of hardware. It is the rare investor who leads with access first and the technology second.
Mistletoe now sits inside a bigger machine: in 2023 Taizo Son and Atsushi Taira co-founded The Edgeof, a Singapore venture group that went on to acquire SoftBank Ventures Asia, and Mistletoe's portfolio is being carried forward through it. Whether water stays a recurring theme or fades as that larger vehicle takes over is the open question, but for now Mistletoe is one of the few Asian family offices treating water access as a deep-tech problem worth its own cheque.
Water Commitment Score
Compiled from official filings, third-party records, and direct intelligence from investors and founders, in Leviathan · recomputed monthly · as of Jun 2026.
How they invest
Portfolio · 2 water companies
Invests alongside
Highlighted = profiled on (don't) Waste Water.
Frequently asked
- What does Mistletoe invest in?
- Mistletoe invests in impact-driven deep-tech startups tackling global challenges across health, food, education, climate and water. Within water it has backed 2 companies that (don't) Waste Water tracks, both focused on decentralized supply: on-site water recycling and pulling drinking water from the air.
- Who is behind Mistletoe?
- Mistletoe is the family office of Taizo Son, a Japanese serial entrepreneur and the youngest brother of SoftBank founder Masayoshi Son. He started it in 2013 with co-founders Atsushi Taira and Hitoshi Miyata, funding it with his own capital rather than raising money from outside investors.
- Is Mistletoe part of SoftBank?
- No. Mistletoe is independent of SoftBank. It was founded by Taizo Son, the younger brother of SoftBank's Masayoshi Son, but runs as his own family office. In 2023 Taizo Son co-founded a separate Singapore group, The Edgeof, which acquired SoftBank Ventures Asia.
- Where is Mistletoe based?
- Mistletoe is headquartered in Tokyo, Japan, in the Minato ward, and was founded there in 2013 by Taizo Son. Its founder later expanded across Asia, and a sister entity he co-founded, The Edgeof, is based in Singapore.
- What stage does Mistletoe invest at?
- Mistletoe backs early-stage companies, investing at Seed and Series A in the water startups it has funded. It tends to come in early on deep-tech founders solving global problems, then support them over time as a patient, founder-friendly family office.