Maruni Woodwork × ONE SAUNA Co-Developed Furniture-Grade Sauna 'kupu sauna' Debuts Worldwide at 'Yunoyama Sosuikyo'

The furniture-grade sauna 'kupu sauna,' jointly developed by 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 sauna brand 'ONE SAUNA'), will be introduced for the first time worldwide at 'Aquaignis Bettei Yunoyama Sosuikyo' (Sosuikyo), a detached villa ryokan operated by Aquaignis Co., Ltd. (Chuo Ward, Tokyo; CEO: Tetsuya Tatehana). The sauna will be installed in two villas: 'Kikoku,' themed around wood, and 'Sekirou,' themed around stone. Prior to its official launch, a press viewing and experience event will be held on-site at Sosuikyo on Thursday, July 2, 2026.

Key Points of This Release

・ World's first installation in an accommodation facility of a 'furniture-grade sauna' developed through a collaboration between Maruni Woodwork, product designer Wataru Kumano, and ONE SAUNA

・ Tailored sauna experiences designed for each villa, aligning with Sosuikyo's room themes

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

・ Equipped with ONE SAUNA's proprietary IoT sauna management system (Patent No. 7510172), enabling automated preheating and automatic heater shutoff with administrator alerts via emergency button, ensuring comfort, energy efficiency, and safety

About kupu sauna

Founded in Hiroshima in 1928, Maruni Woodwork has championed the concept of 'industrialized craftsmanship,' creating products beloved by architects and designers worldwide. To apply its furniture manufacturing expertise in woodworking to the extreme environment of saunas—exposed to heat and steam—product designer Wataru Kumano (principal of design office kumano) and ONE SAUNA, possessing expertise in thermal and sensory design for saunas, have joined forces.

The resulting 'kupu sauna' achieves both furniture-level finishing precision and the functional and aesthetic beauty of product design. Its signature half-dome curved structure allows steam generated during löyly to circulate along the dome's inner curves, softly descending onto bathers' backs for a one-of-a-kind sensory experience.

kupu sauna layout

Design focused on heat circulation

kupu sauna can be installed indoors

Overview of Installation at Sosuikyo – Themed Sauna Experiences

'Aquaignis Bettei Yunoyama Sosuikyo' is a ryokan with 12 detached villas, each themed around natural materials, offering guests 100% natural flowing hot spring baths and premium cuisine. In line with this concept, 'kupu sauna' will be introduced into the two villas 'Kikoku' and 'Sekirou'.

▼ Wood-themed Villa 'Kikoku (Kino Toki)'

Wood-themed Villa 'Kikoku (Kino Toki)'

・ Pathway design leading from a wooden deck to the sauna

・ Equipped with Maruni Woodwork's relaxation chair 'kupu sauna Chair'

▼ Stone-themed Villa 'Sekirou (Sekirou)'

Stone-themed Villa 'Sekirou (Sekirou)'

・ Features a stone cold bath, enabling a full-cycle experience: sauna → stone cold bath → outdoor cooling

・ Equipped with Maruni Woodwork's relaxation chair 'kupu sauna Chair'

ONE SAUNA / Local Production for Local Consumption Sauna Concept

ONE SAUNA operates on the concept of 'local production for local consumption,' running saunas across six locations in Japan using locally sourced wood. For this 'kupu sauna,' 'Yoshino Hinoki' from Nara is used. The soft texture and balanced thermal properties of Yoshino Hinoki are maximized through furniture-grade finishing.

※ ONE SAUNA received the 2020 Good Design Award.

IoT Sauna Management System (Patent No. 7510172)

The 'kupu sauna' is equipped with ONE SAUNA's patented proprietary IoT sauna management system (Patent No. 7510172).

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

・ Ensures optimal temperature is always maintained upon guest check-in, delivering a premium customer experience

・ In case of emergency button activation in the room, the heater is automatically shut off and an automatic phone alert is sent to the manager, enabling immediate response

This 'heat only when and as much as needed' operation enables both high-quality guest experiences and sustainable operations for accommodation facilities.

Press Viewing and Experience Event

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

Venue: Aquaignis Bettei Yunoyama Sosuikyo

4842-1 Komono, Komono-cho, Mie-gun, Mie Prefecture 510-1233

Program: Opening remarks, Q&A, photo session, followed by guided tours of the 'Kikoku' and 'Sekirou' villas and bathing experience in the 'kupu sauna'.

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

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

Tetsuya Tatehana, CEO, Aquaignis Co., Ltd.

Schedule:

11:00　Opening remarks and Q&A

11:30　Villa tour 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　Event ends

Registration: https://forms.gle/Du6pTQEjZpPWL44r6

Company Profiles

▼ Aquaignis Co., Ltd.

・Head Office: 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 Name: Aquaignis Bettei Yunoyama Sosuikyo

・Facility Location: 4842-1 Komono, Komono-cho, Mie-gun, Mie Prefecture

・Facility URL: https://sosuikyo.com/

▼ Maruni Woodwork Co., Ltd.

・Location: 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)

・Location: 7275-1 Kaejita, Miyazaki City, Miyazaki Prefecture

・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/