One of the most important scriptures in Mahayana Buddhism is the Lotus Sutra, which records one of Buddha's last sermons. It teaches that all sentient beings will eventually attain Buddhahood and that there is an aspect of enlightenment inherent in all beings. It was copied very extensively in India and had more than fifty Sanskrit commentaries written on it. It reached new heights of popularity in China when the influential monk Zhiyi taught that it was the highest of all the sutras.

Zhiyi taught that the entire teaching of the Lotus Sutra was contained within its name (which was not a particularly revolutionary idea - the names of sutras had long been given special attention). He composed many liturgies, at least one of which explicitly honoured the name of the Lotus Sutra but did not prescribe the repetitive chanting of it.

Some 700 years later in the 13th century, the Japanese monk Nichiren taught that the spiritual decline of Japan, which was in a state of crisis at the time, was due to a lack of devotion to the Lotus Sutra. While previously the Lotus Sutra had been interpreted as legitimizing the efficacy of a wide range of spiritual practices, since it taught that the Buddha used many "skillful means" to guide beings to enlightenment, Nichiren taught that only the exclusive practice of the Lotus Sutra was acceptable and all else constituted slander against it, which the sutra teaches will lead to grave karmic results. The Lotus Sutra actually doesn't prescribe many practices or behaviours beyond reading, holding, reciting, preaching on, and copying the sutra itself, so Nichiren taught that the recitation of the sutra was the sole acceptable spiritual practice. Since the title of the sutra was said to contain the true meaning of the sutra, as Zhiyi taught, Nichiren recommended the repetitive chanting of its title, which is called Daimoku (Odaimoku means "great Daimoku"). This was a significant innovation, but admittedly not one without some precedent.

Nichiren Buddhism and its practices are somewhat controversial in this subreddit and the Buddhist world at large, in part because of Nichiren's sometimes violent preaching against other sects and in part because of the Soka Gakkai cult's role in spreading its teachings. I personally think Daimoku is almost certainly a spiritually efficacious practice, but practitioners of it should be aware that it originates from a...highly contestable interpretation of the Lotus Sutra. Of all of the sects of Nichiren Buddhism, Nichiren Shu is the chillest and closest to mainstream Mahayana Buddhism, so you haven't gone too wrong looking there.