Open PCSX2, go to Config > Plugin/BIOS Selector , and click the BIOS tab. Refresh the list and select the Japanese v2.30 entry.
Download a tool like "PS2 BIOS Dumper" and put it on a USB drive formatted to FAT32. Ps2 Bios Japan Scph-90000 Download
This BIOS is region-locked to Japan (NTSC-J), meaning it is required to boot Japanese imports or navigate the original Japanese system menus. Open PCSX2, go to Config > Plugin/BIOS Selector
It is the most "refined" version of the PS2 code, featuring the final updates Sony made to the console's internal OS. go to Config > Plugin/BIOS Selector