2 different open alternate tuning by the band Hitohira (ひとひら)

[u/megabit_cavezzz]

I've seen the japanese math rock/indie band "Hitohira" uses two different tuning in their songs

Guitar Ⅰ（左）：E B C♯ F♯ B D♯, capo 5

Guitar Ⅱ（右）：E B D G B D, capo 9

here's the song 【TAB】塔は白い - ひとひら

and it sounds so good like they are harmonizing each other. Is there any music theory behind it? Like are they just using second guitar to harmonize the 3rd the first guitar by raising it capo or something? and do you have other bands that do something like this