KAI, the onsen ryokan brand by Hoshino Resorts, is pleased to announce the grand opening of KAI Zao in Zao Onsen, Yamagata Prefecture, on October 15, 2026. In anticipation of this debut, reservations will be accepted starting April 22, 2026. The property has designed a “spiral journey” to onsen rejuvenation, drawing inspiration from Zao’s iconic "Okama" crater lake. Utilizing the region's uniquely high-acidity hot spring water—among the most potent in Japan—the property features a circular wellness area designed for guests to traverse between hot spring baths, saunas, and Jacuzzis, offering a holistic experience that revitalizes both body and mind.
About KAI Zao
The Zao area in Yamagata prefecture has long been recognized as a center for mountain worship, serving as a sanctuary where ascetic practitioners would travel to purify their minds and bodies. Zao Onsen, in turn, has been cherished for generations for its unique properties; it washes away dead skin cells and impurities, effectively polishing the skin to reveal a smooth, healthy complexion. Drawing inspiration from both this rich history and the restorative power of its waters, KAI Zao seeks to synthesize these elements into a singular experience. By redefining Zao as a premier wellness destination that offers year-round opportunities for introspection and realignment—far beyond its seasonal reputation for winter skiing—KAI Zao proposes a deeply restorative stay tailored to the needs of the discerning traveler.
Signature Feature 1: A Spiral Journey to Onsen Bliss—Circulating Through Famous Waters and Breathtaking Views to Reach the Pinnacle of Rejuvenation
The property features a circular, traversable wellness area designed to integrate guests with the natural environment of Zao. Beyond traditional bathing in the region’s famous high-acidity waters across various concentrations, guests can freely traverse an area equipped with saunas and lounges to pursue their own personal path to rejuvenation. This concept of a circular journey is inspired by the history of Zao as a center of mountain worship, where practitioners would purify their body and mind as they climbed the mountain step by step. As guests travel up the tower-style ryokan in a spiral motion, the process washes away the busyness and stress of daily life, clearing the path to relax the mind and body. At the summit of this journey awaits a rooftop terrace, offering 360-degree panoramic views and a Jacuzzi with soft steam inspired by the local "Okama" crater lake. It is the final destination where the mind and body are liberated, and the rejuvenation achieved through this spiral journey is fully realized.
Signature Feature 2: The "Crimson Modern Rooms”—A Celebration of Safflower Hues and Yamagata Craftsmanship
Each KAI property features “KAI Signature Rooms" designed to immerse guests in the unique character of its surroundings. For KAI Zao, the guest room theme centers on the vibrant "Safflower" —a historic symbol of Yamagata—resulting in the "Crimson Modern Room’. These spaces are adorned with fine examples of local craftsmanship, including Safflower-dyed Washi paper, luxurious "Yamagata Dantsu" hand-woven textile, and bespoke furniture commissioned from Tendo Mokko Carpentry, all harmonizing to create a modern and deeply comfortable atmosphere. Each of the 49 rooms is equipped with expansive panoramic windows. From the comfort of their own private retreat, guests can claim the breathtaking scenery of Zao for themselves, enjoying an intimate view of the passage of time as the landscape transforms through the changing seasons.
All 49 guest rooms are designated as "Crimson Modern Rooms.”
Safflower-dyed Washi paper lanterns and Yamagata Dantsu textile art.
Guest room outdoor baths with decorative accents
Signature Feature 3: The "Benibana Sansai Kaiseki"—Nourishing the Body and Restoring Beauty
The "Benibana Sansai Kaiseki" (Safflower & Wild Vegetable Course) was born from the sophisticated aesthetic sensibility of historical Safflower merchants, who channeled their desire to provide the finest hospitality to their cherished guests into every dish. The dining experience begins with the eye-catching "Houraku-mori (appetizer assortment)," served on vibrant vermilion-lacquered tableware, featuring an array of rare heirloom vegetables and delicate items prepared with vinegar that glide smoothly on the palate.
The main course, "Gassan Nabe," is a hot pot named after one of Yamagata’s most iconic sacred mountains. It features a rich harvest of forest ingredients, including seri (Japanese parsley), wild vegetables, yamabushitake (lion's mane) mushrooms, and hanabiratake (cauliflower mushrooms), paired with succulent duck. The broth, infused with the savory essence of mokuzu crab, harmonizes perfectly with the rich duck fat and mushrooms, creating an explosion of umami with every bite—a truly surprising and deep culinary delight.
The appetizer assortment of the "Benibana Sansai Kaiseki."
Main Dish - Gassan Nabe
Dessert - Safflower and Pear Panna Cotta.
Property and Project Overview
Property Details
Property Name: KAI Zao
Total Guest Rooms: 49 rooms
On-site Facilities: Front desk, public bath, dining area, rooftop terrace, boutique shop, etc.
Site Area: 6,320.03 square meters
Building Footprint: 1,212.53 square meters
Total Floor Area: 6,127.29 square meters
Opening Date: October 15, 2026
Reservation Commencement: April 22, 2026
Design and Construction
Architectural Basic Design & Design Supervision: Shuhei Kamiya + Kamiya Architects
Landscape Design: Oryza Inc.
Execution Design & Supervision: Ken Asai Architects & Associates
Construction: Ichimura Komuten Co., Ltd.
Architect's Comment: Shuhei Kamiya
"I aimed to create architecture that embodies the culture, climate, and topography of Zao. Drawing cues from the scenery of the Okama crater, the memories of mountain worship, and the physical sensations of being in an onsen district, I shaped the overall design through continuous dialogue with many local makers and craftsmen. I hope this becomes a place where guests can encounter experiences unique to this land throughout all four seasons, not just in winter."
About the "Hoshino Resorts Tourism Revitalization Fund"
Hoshino Resorts and RISA Partners, Inc. established a fund on October 30, 2020, to invest in domestic lodging facilities, which they have been operating since its inception. Through this Tourism Revitalization Fund, both organizations aim to invest in high-quality tourism destinations across Japan, thereby contributing to the growth and development of the nation's tourism and lodging industries. "KAI Zao" serves as the third project under this fund, following "KAI Okuhida" in the Okuhida Onsen-go area of Gifu Prefecture and "KAI Akiu" in the Akiu Onsen area of Miyagi Prefecture.
About KAI Brand
Onsen Ryokan loved by local and overseas travelers
KAI is a leading brand of onsen ryokan where every establishment offers a contemporary take on traditional Japanese inn whilst keeping Western comforts. KAI invites one to discover the multifaceted aspects of Japan through natural hot springs, exploration of local arts and entertainment, and classic Kaiseki-style course meals using local and seasonal flavors. Experience Washoku, Japanese cuisine, presented on carefully selected ceramics for full exposure to culinary sensations.
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