KAI, a leading onsen ryokan brand by Hoshino Resorts, will open KAI Zao in Zao Onsen, Yamagata Prefecture, in fall 2026, marking the company’s first venture into the region. Surrounded by the majestic Zao Mountain Range, the ryokan will feature a panorama rooftop terrace inspired by Mount Zao’s iconic "Okama" crater lake. Guests will be invited to explore breathtaking mountain views and soothing hot spring baths in harmony with nature. KAI Zao represents the third project under the Hoshino Resorts Tourism Revitalization Investment Limited Partnership (hereafter, the “Hoshino Resorts Tourism Revitalization Fund”), a fund jointly established in October 2020 by Hoshino Resorts and RISA Partners, Inc.
About Zao Onsen
Zao Onsen is a hot spring destination with a history of over 1,900 years. Often called the “Hot Spring Village in the Sky,” it sits 880 meters above sea level at the foot of the Zao Mountain Range. Known for its highly acidic sulfur springs, the springs draw from volcanic sources symbolized by "Okama," a crater lake also known as Goshikinuma (“Five-Color Marsh”). Zao Onsen beautifully blends a rich history, powerful spring waters, and breathtaking natural scenery.
Features of KAI Zao
1. Rooftop Terrace with 360° Views
Inspired by "Okama," this rooftop terrace offers breathtaking 360-degree views. Guests can take in panoramic scenery, from the Zao Mountain Range in the east to the Asahi Mountains in the west, with tranquil rural landscape in between. A central jacuzzi, surrounded by alpine plants native to Zao, invites guests to soak while enjoying the ever-changing scenery. Seating areas throughout the terrace offer peaceful moments to connect with nature.
2. Public Bath Featuring Zao Onsen’s Sulfur Springs
Located adjacent to the guest rooms, the dedicated bathhouse features a public hot spring designed to maximize the therapeutic benefits of Zao Onsen’s renowned highly acidic sulfur springs. It contains three distinct tubs with varying mineral concentrations, allowing guests to enjoy a staged soaking experience. A garden of local Zao stones stretches in front of the open-air bath, providing a peaceful setting to soak amid the changing seasons. This tranquil retreat contrasts with the dramatic rooftop terrace views, creating a serene and immersive hot spring experience.
Facility Overview
Facility Name: KAI Zao
Rooms: 49 rooms
On-Site Facilities: Front Desk, Public Hot Spring, Dining Area, Rooftop Terrace, Shop, etc. (for guests only) *Contents are subject to change.
Site Area: 6,320.03 m²
Building Area: 1,212.53 m²
Total Floor Area: 6,127.29 m²
Opening Date: Fall 2026 (Planned)
Reservations Start: Undecided *Details to be announced later
Architectural Basic Design/Design Supervision: Shuhei Kamiya + Kamiya Architects
Landscape Design: ORYZA Co., Ltd.
Design/Supervision: Ken Asai Architecture Institute Co., Ltd.
Construction: Ichimura Komuten Co., Ltd.
About the "Hoshino Resorts Tourism Revitalization Fund"
On October 30, 2020, Hoshino Resorts and RISA Partners, Inc. formed and began operating an investment fund targeting domestic accommodation facilities. Through the Hoshino Resorts Tourism Revitalization Fund, the two companies aim to invest in prime tourist destinations across Japan, thereby contributing to the growth of Japan's tourism and accommodation industry. KAI Zao follows KAI Okuhida (Okuhida Onsen, Gifu Prefecture) and KAI Akiu (Akiu Onsen, Miyagi Prefecture) as the fund’s third investment project.
About KAI
KAI is Hoshino Resorts' onsen ryokan (traditional Japanese hot spring inn) brand well loved by local and overseas travelers. With 23 properties across Japan, KAI aims to provide hospitality that meets modern needs while preserving the beauty of the seasons, Japanese aesthetics, locality and traditions of the different regions. KAI Cultural Discovery, a key feature of the brand, offers guests experiences of local traditional culture and crafts, while KAI Signature Rooms (guest rooms) are designed to reflect the unique culture of each region. In 2026, KAI plans the opening of three new facilities: KAI Kusatsu (Kusatsu Onsen, Gunma Prefecture), KAI Miyajima (Miyajima Onsen, Hiroshima Prefecture), and KAI Zao (Zao Onsen, Yamagata Prefecture), as well as the renewal of KAI Matsumoto (Asama Onsen, Nagano Prefecture).
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