The story
Niigata Television Network 21 was established on March 7, 1983 and commenced transmissions at 6:10am on October 1, 1983. Prior to that, TV Asahi programming was seen on NST. NST was affiliated to FNN/FNS, NNN/NNS and ANN, before alleviating the station's network schedule with the launch of TNN (now TeNY), which took over the NNN affiliation in 1981 and NT21, which took over the ANN affiliation in 1983. By then, Niigata has four network stations.
Digital terrestrial test transmissions commenced on August 1, 2006. To mark the occasion, NT21 was rebranded as ux. A full license for digital terrestrial television was granted on September 25, starting on October 1. Aside from airing TV Asahi shows, the station also currently airs a few TV Tokyo shows, since the network does not have a station in most prefectures.
From Wikipedia’s article on Niigata Television Network 21, shared under CC BY-SA 4.0.4