Emulator

According to Dolphin, NTSC-U BIOS is different than NTSC-J, so when you put an "NTSC-J" BIOS in /GC/USA/ it'll complain that it's a JAP IPL
https://github.com/dolphin-emu/dolphin/blob/master/Source/Core/Core/Boot/Boot.cpp#L204-L223

According to redump/MAME, however, NTSC-U and NTSC-J are the same BIOS, and the NTSC-U BIOS hash that's been used has garbage in the last 0x8000 bytes
https://git.redump.net/mame/diff/src/mame/drivers/gamecube.cpp?id=ec3caa98bdcab04b0cb90b3cf1c1eb740433dfd6
http://redump.org/datfile/gc-bios/

After bringing it up on IRC,

<Extrems> Yeah, US and Japan are the same.
<Extrems> The only hardware difference between them is a resistor's location.

There's an older issue at https://bugs.dolphin-emu.org/issues/10113 but doesn't have enough information to solve it.

Will probably have to fix up the wiki too (found this while googling for info) https://wiki.dolphin-emu.org/index.php?title=Template:Problems/GC_Font