Although the term “Rinne Tensei” became well-known as a manga series like Naruto, Demon Slayer and Jujutsu Kaisen, which gained popularity worldwide, not many people know its origins. Rinne Tensei (輪廻転生), originally derived from the Sanskrit idea of “Samsara,” is a Buddhist concept that refers to the cycle of rebirth and reincarnation. It is believed in Buddhist teachings that all living beings are subject to the law of cause and effect and that their actions in this life will determine their rebirth in the next. Rinne Tensei is seen as a continuous cycle of birth, death and resurrection, which can be broken only by attaining enlightenment and escaping the cycle of suffering, or in other words, going to Buddhist paradise.
"Densetsu" (伝説) is a Japanese word that means "tradition, legend, or folklore". It can also mean "explanations of tradition".They are also narratives of Japanese tradition describing acts of prominent figures, especially holy men who have attained religious powers and are not entirely legendary (i.e. they had historical existence). Most of them are Buddhist. Particularly well-known are Kobo densetsu, the tales of Kūkai. Comparable as genres of religious stories are engi (which tell especially of miracles and portentous events associated with holy places) and reigenki (stories of Buddhas and bodhisattvas, in particular, of their efficacious powers of intercession).
The Japanese word mugen (無限) can mean "dream", "fantasy", or "infinite". It can also mean "unlimited" or "vast". The Bell of Mugen is a bell in a Japanese ghost story. In the story, the bell's ringing becomes an affliction, and the priests roll it down a hill into a swamp. The swamp swallows up the bell, and it's lost forever. In the legend, the bell is called the Mugen-Kane. The story goes that the bell is made of bronze, silver, and gold. It's said to carry prayers to, Takamagahara (高天原). In Japanese mythology it is the Shinto version of heaven. It's also known as the "Plane of High Heaven" or "High Plane of Heaven".