Summary
-------

> How do these relate to the fonts at https://mplus-fonts.osdn.jp/?

M+ font ( https://mplus-fonts.osdn.jp/ ) has currently 5000 glyphs(characters) of Japanese Kanji characters, but not enough.

IPA Gothic font ( http://ipafont.ipa.go.jp/ ) has 11000 Kanji glyphs.

MigMix, Migu are mixed fonts with M+ and IPA Gothic font.

M+..+IPAG are old versions of mixed fonts with M+ and IPA Gothic font.



Relation
--------

> M+1P+IPAG-circle.ttf ...
> How do these relate to MigMix and Migu?


M+??+IPAG-circle.ttf -> new version -> Migu
M+??+IPAG.ttf -> new version -> MigMix


specifically..

M+1P+IPAG-circle.ttf
new version -> Migu 1P

M+1P+IPAG.ttf
-> MigMix 1P

M+1VM+IPAG-circle.ttf
-> Migu 1M

M+2P+IPAG-circle.ttf
-> (not build)

M+2P+IPAG.ttf
-> MigMix 2P

M+2VM+IPAG-circle.ttf
-> Migu 2M

ipag.ttf (IPA Gothic font)
not distributed in this site. You can get it from http://ipafont.ipa.go.jp/

ipagp.ttf (IPA P Gothic font)
ipagui.ttf (IPA Gothic UI font)
ipam.ttf (IPA Mincho font)
ipamp.ttf (IPA P Mincho font)
You can get them from http://ipafont.ipa.go.jp/



Package
-------

> Should I replace the above fonts with MigMix and Migu,
> or should I create a new package containing MigMix and Migu?

I recommend creating a new package, but care with license.
The license of MigMix, Migu is 'IPA Font License', differs from mixfont-mplus-ipa-TrueType-20060520.

IPA Font License v1.0 https://opensource.org/licenses/IPA

Please check these packages.
https://aur.archlinux.org/packages/ttf-migmix/
https://aur.archlinux.org/packages/ttf-migu/
https://svnweb.freebsd.org/ports/head/japanese/font-migmix/
https://svnweb.freebsd.org/ports/head/japanese/font-migu/
https://packages.debian.org/sid/fonts-migmix

Thanks.