Maruni Woodwork × ONE SAUNA Co-Develop High-End Furniture-Grade Sauna 'kupu sauna' — World's First Installation at 'Yunoyama Sosuikyo' with Unique Experiences in Wooden 'Kikoku' and Stone-Themed 'Sekirou' Villas

Maruni Woodwork Co., Ltd. (Hiroshima City, Hiroshima Prefecture; President & CEO: Yo Yamanaka) and Libertyship Co., Ltd. (Miyazaki City, Miyazaki Prefecture; CEO: Haruya Agematsu, operator of the sauna brand 'ONE SAUNA') have jointly developed a furniture-grade sauna called 'kupu sauna.' It has been decided that this sauna will be introduced for the first time in the world at 'Aquaignis Bettei Yunoyama Sosuikyo (Sosuikyo),' a detached villa resort operated by Aquaignis Co., Ltd. (Chuo Ward, Tokyo; CEO: Tetsuya Tatehana). The sauna will be installed in two villas: 'Kikoku (Kino-toki),' themed around wood, and 'Sekirou (Sekirou),' themed around stone. Prior to its official launch, a press preview and experience event will be held on-site at Sosuikyo on Thursday, July 2, 2026.

Key Points of This Release

World's first installation of a 'furniture-grade sauna' at a lodging facility, resulting from the collaboration between renowned furniture maker Maruni Woodwork, product designer Wataru Kumano, and ONE SAUNA

Unique sauna experiences designed for each villa, aligned with Sosuikyo's room themes: 'Kikoku' and 'Sekirou'

ONE SAUNA, winner of the 2020 Good Design Award, continues its philosophy of 'local production, local consumption' by using Yoshino Hinoki cypress from Nara

Equipped with ONE SAUNA's proprietary, patented IoT sauna management system (Patent No. 7510172), enabling automated preheating, automatic heater shutdown linked to emergency buttons, and automatic administrator alerts—ensuring comfort, energy efficiency, and safety

About 'kupu sauna'

Founded in Hiroshima in 1928, Maruni Woodwork has long championed the concept of 'industrialized craftsmanship,' creating products beloved by architects and designers worldwide. To apply its advanced woodworking techniques—honed through furniture manufacturing—to the extreme environment of saunas, exposed to heat and steam, the company collaborated with product designer Wataru Kumano (founder of design office kumano) and ONE SAUNA, which possesses expertise in thermal and sensory design for saunas.

The result is 'kupu sauna,' a sauna that achieves both furniture-level finishing precision and the functional and aesthetic beauty envisioned by a product designer. Its defining feature is a half-dome curved structure, where steam generated during löyly circulates along the curved inner surface of the dome and gently descends onto bathers' backs, creating a one-of-a-kind sensory experience.

Overview of Installation at Sosuikyo — Sauna Experiences by Room Theme

'Yunoyama Sosuikyo,' operated by Aquaignis, is a resort of 12 detached villas, each designed around natural materials, offering guests 100% free-flowing natural hot spring baths and premium dining. In line with the resort's unique material-based themes, 'kupu sauna' will be installed in two villas: 'Kikoku' and 'Sekirou,' enhancing their distinct atmospheres.

Wood-Themed Villa 'Kikoku (Kino-toki)'

- A seamless circulation path leads from a wooden deck directly into the sauna

- Equipped with Maruni's 'kupu sauna chair,' designed for post-sauna relaxation

Stone-Themed Villa 'Sekirou (Sekirou)'

- Features a stone cold plunge pool, enabling a full cycle of sauna → stone cold bath → outdoor cooling

- Equipped with Maruni's 'kupu sauna chair,' designed for post-sauna relaxation

ONE SAUNA / Local Production, Local Consumption Sauna Philosophy

ONE SAUNA operates under the concept of 'local production, local consumption,' developing saunas using regionally sourced timber across six locations in Japan. For this 'kupu sauna,' 'Yoshino Hinoki' from Nara has been selected. The soft texture and balanced thermal properties of Yoshino Hinoki—resistant to overheating—are maximized through furniture-grade craftsmanship. *ONE SAUNA received the 2020 Good Design Award.

IoT Sauna Management System (Patent No. 7510172)

'kupu sauna' is equipped with ONE SAUNA's patented IoT sauna management system (Patent No. 7510172), developed in-house.

Automated preheating synchronized with reservation data optimizes operation time and enables energy-efficient management

Ensures the sauna is always at the ideal temperature upon guest check-in, delivering a premium customer experience

When the emergency button inside the room is pressed, the heater is automatically shut off and an automatic phone alert is sent to the manager, enabling immediate response in emergencies

This 'heat only when and as much as needed' operation model enables both high-quality guest experiences and sustainable, eco-friendly operations for lodging facilities

Press Preview and Experience Event Information

Date | Thursday, July 2, 2026, 11:00–14:30

Venue | Aquaignis Bettei Yunoyama Sosuikyo, 4842-1 Komono, Komono-cho, Mie District, Mie Prefecture 510-1233

Program | Includes welcome remarks, Q&A session, photo session, as well as guided tours of the 'Kikoku' and 'Sekirou' villas and bathing experiences in the 'kupu sauna.'

Speakers (tentative, titles omitted) |

Yo Yamanaka, President & CEO, Maruni Woodwork Co., Ltd.

Haruya Agematsu, CEO, Libertyship Co., Ltd. (ONE SAUNA)

Tetsuya Tatehana, CEO, Aquaignis Co., Ltd.

Event Schedule |

11:00 Welcome remarks and Q&A

11:30 Villa tours and facility photography

12:30–13:15 kupu sauna bathing experience① (Kikoku: male / Sekirou: female)

13:30–14:15 kupu sauna bathing experience② (Kikoku: female / Sekirou: male)

14:30 Conclusion

Press Registration Form

Company Overview

Maruni Woodwork Co., Ltd.

Headquarters: 24 Shirasuna, Yuki-cho, Saeki-ku, Hiroshima City, Hiroshima Prefecture

Founded: 1928

Representative: President & CEO Yo Yamanaka

Business: Planning, manufacturing, and sales of furniture

URL: https://www.maruni.com/

Libertyship Co., Ltd. (ONE SAUNA)

Headquarters: 7275-1 Kaejita, Miyazaki City, Miyazaki Prefecture, Kodomo no Kuni

Representative: CEO Haruya Agematsu

Business: Sauna development and operation, sauna facility production, provision of IoT sauna management system 'ONE SAUNA'

Brand URL: https://onesauna.jp/

Corporate URL: https://libertyship.jp/

Aquaignis Co., Ltd.

Headquarters: 7F, Yoda Tadashi Building, 1-14-9 Kyobashi, Chuo Ward, Tokyo

Representative: CEO Tetsuya Tatehana

Business: Food and beverage, hot spring facilities, confectionery manufacturing, real estate

Corporate URL: https://aquaignis-company.jp/

Facility Overview

Yunoyama Sosuikyo (Yunoyama Sosuikyo)

https://sosuikyo.com/ Opened in July 2020 as a detached villa resort under the Aquaignis brand, located at the foot of Yunoyama Onsen. Guests can enjoy supreme natural hot springs and luxurious dining. The 12 villas are themed around eight naturally beautiful materials: soil, stone, plaster, wood, lacquer, washi paper, glass, and iron. The spaces, adorned with contemporary art, crafts, antique art, and antiques, feel like an exceptionally comfortable art museum. Enjoy a luxurious time surrounded by authentic materials and art.

Number of Rooms | 12 villas Parking | 50 spaces

Address | 4842-1 Komono, Komono-cho, Mie District, Mie Prefecture 510-1233

Access | 5-minute walk from 'Yunoyama Onsen Station' on the Kintetsu Yunoyama Line; 5-minute drive from 'Komono IC (ETC only)' on the Shin-Meishin Expressway

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