During the winter months, Kushiro Marshland in eastern Hokkaido, Japan, is home to the celebrated red-crowned crane or "tancho". As temperatures plunge, these cranes flock to the marshland where an underground spring provides warmth and prevents the water from freezing, and the local people provide food to nurture the birds back from the brink of extinction. These mass gatherings are fraught affairs with limited space and predators close by, but as winter progresses one of nature's most spectacular courtship rituals begins where courting birds mirror each other's movements in graceful, spellbinding displays that can last for days. Against the ever-changing backdrop of Japan's great marshland, a love story unfolds.