The official statement published on the band’s website states that in the month of September 2018, a law firm sent mail addressed to ka-yu. The contents were serious enough to put ka-yu’s activities to a halt, however, details on the letter contents could not be disclosed as there is a possibility that it could be taken to court in the future.
This situation created conflicts between ka-yu and the other band members but they concluded that he had done nothing that “transgressed the law”. After a lengthy discussion, the band explained to ka-yu that he needed to prove his innocence while focusing on musical activities. However, ka-yu decided that even though Janne Da Arc was important to him, there was something more he wanted to protect, resulting in his departure.
Amongst all this, there were other uncertainties that lead to the final decision of Janne Da Arc disbandment. One was the uncertainty surrounding vocalist yasu, also of Acid Black Cherry, and his still on-going recovery from health issues that lead him to his hiatus in 2017. Another was a matter of feeling that they could not continue as a four-member band—thus they decided to disband.
I never read about why JDA disbanded, that’s wierd af