Hi Hayato,
I am no expert, but here's my setup, hopefully it can help you:
1. I am using OLED vita handheld with enso, but theoretically should work on pstv (enso) with usb.
2. SD2Vita 128gb formatted exfat. PSVD 128gb formatted exfat.
3. Download gamesd.skprx from
https://github.com/xyzz/gamecard-microsd/releases
4. Download and install usbmc (v4) from
https://github.com/yifanlu/usbmc/releases
5. Once usbmc vpk is installed, run the USBMC application once to install the skprx and I think USBMC app will disable the 3G module errors because the modem is now gone. The application will restart your vita. I did not need to run it a second time to copy files or anything.
6. My config.txt in ur0:tai/config.txt is (I have no files in urx0:tai/, directory is empty):
# This file is used as an alternative if ux0:tai/config.txt is not found.
# For users plugins, you must refresh taiHEN from HENkaku Settings for
# changes to take place.
# For kernel plugins, you must reboot for changes to take place.
*KERNEL
ur0:tai/gamesd.skprx
ur0:tai/nonpdrm.skprx
ux0:app/PSPEMUCFW/sce_module/adrenaline_kernel.skprx
# henkaku.skprx is hard-coded to load and is not listed here
*main
# main is a special titleid for SceShell
ur0:tai/henkaku.suprx
*NPXS10015
# this is for modifying the version string
ur0:tai/henkaku.suprx
*NPXS10016
# this is for modifying the version string in settings widget
ur0:tai/henkaku.suprx
*KERNEL
ur0:tai/usbmc.skprx
7. Install and run Vitashell 1.74 and press "Triangle button" to mount PSVD as uma0
That's all. Critical component is step 3 and 5. It has to be those files.
Hope that helps. Please let me know!