D-did Kajiura already spoiled the one in charge of OP/ED for Kimetsu no Yaiba? And she will be handling the composition?? This is purely speculation but I don't see any reason why she would go to a concert of them suddenly then I remembered the picture uploaded by Kugayama of Highway Star artists...
Yasunori Mori(former agent of Kajiura from spacecraft but still working with her until now) - Executive staff of Highway Star -> OLDCODEX etc. were handled by the said management -> OP Theme song artist of God Eater -> Anime done by ufotable -> ufotable in charge of Kimetsu no Yaiba -> music by Kajiura and Shiina
Two problems tho: it's a male band(lol) and depends if they will use lantis/sony music artist for the anime. And remember that time when she went to SH concert where Joelle is kind of surfacing around Kajiura due to LORD? What I'm trying to say is that she won't go to some concert if there's no meaning behind it. PURELY SPECULATION THOUGH but kind of interesting tweet haha
That was Hironobu Kagayama singing Lacrimosa with Kalafina on Anipara Ongakukan, Masaaki Endoh has sung Uninstall with Chiaki Ishikawa on the same programme and solo (with Chiaki-san on chorus?) on one of his ENSON cover albums.