The Rainy Season Festival (Dế khừ chà) is one of the important festivals of the Ha Nhi people in Dien Bien province. In the province, there are over 5,500 Ha Nhi people, living concentrated in four border communes of Muong Nha district: Sin Thau, Sen Thuong, Chung Chai, and Leng Su Sin (now Sin Thau commune, Muong Nha district). In recent years, along with the development of economic life, the Ha Nhi people have still preserved and promoted their unique traditional cultural values.

The Rainy Season Festival is held annually in the fifth lunar month, when the main planting season begins. This is an occasion for the Ha Nhi people to pray for favorable weather, a bountiful harvest, thriving livestock, healthy children, and ancestral blessings for a prosperous village.

The date for the festival is decided by the community, usually chosen as the day of the Pig or the day of the Dragon. Before the festival, women prepare banana leaves and soak sticky rice. At dawn on Tet (Lunar New Year), the whole family steams sticky rice, pounds rice cakes, and shapes three cakes to offer to their ancestors, expressing the fruits of their labor and gratitude to their grandparents and ancestors. After the offering of rice cakes comes the ritual of summoning spirits, with traditional offerings such as chicken, eggs, water, wine, and jewelry and clothing of family members, praying for health and peace. This is followed by the ritual of worshipping ancestors from both the paternal and maternal sides, then the whole family celebrates Tet, inviting relatives, friends, and neighbors to join in the festivities. The rainy season Tet lasts for four days, associated with days of taboo according to traditional beliefs. During these days, the Ha Nhi people celebrate, dance, sing, and participate in folk games such as swinging, creating a warm and lively festive atmosphere – also a time to rest after a period of hard work. Visiting Muong Nha in May or June, tourists will have the opportunity to immerse themselves in the atmosphere of the Ha Nhi people's Rainy Season Tet, experience the beauty of the local culture, enjoy traditional cuisine, and feel the simplicity and hospitality of the people in this westernmost border region of the country.