There's technically no real sense of a TV season like in the USA system. There are 4 seasons of broadcast ranges: Winter, Spring, Summer, Autumn. All are 3-month ranges. And there has been anime that has only aired 12-13 episodes for its entire season. Sentai and Kamen Rider run a new season every year. Some shows may have a season of only 12 or 13 episodes. Some may have for 25-26, 50-52, etc.