maybe not quite a cult but the United Red Army were pretty wack.

The United Red Army had 29 members and lost 14 by killing them in less than a year. Most were members of the New Left.

[...]

the group underwent a process known as ‘self-criticism’, a ritual that had become normalized among Left groups in Japan at the time. The original intention of this practice was to allow members of the group to strengthen their alignment with the values and purpose of the cause

However, Mori quickly introduced an element of violence to this process in keeping with the New Left’s demand for individuals to demonstrate their commitment. The purpose of this violence against members was to test their devotion to the cause. Mori argued that beating members into unconsciousness would allow for them to be reborn with true "communistic subjectivity" when they were brought back to consciousness.

[...]

These violent beatings ultimately saw the death of 12 members of the URA who had been deemed not sufficiently revolutionary. Many of the twelve victims died tied to posts in the open, exposed to the elements, but others were beaten to death or slaughtered with knives.