Since the nippon_ichi tag is applied very irregularly, it'd probably make sense for the games they developed to imply nippon_ichi. I believe this is all of them that are on danbooru (with disgaea already being implied by the individual games):
disgaea la_pucelle phantom_kingdom prinny_can_i_really_be_the_hero? phantom_brave rhapsody marl_kingdom soul_cradle hayarigami infiniteloop antiphona_no_seikahime

I don't know if we'd want to imply nippon_ichi from games they published in Japan or not, but if so:
criminal_girls classic_dungeon grimgrimoire tori_no_hoshi a_witch's_tale last_rebellion blue_roses

Also, on a related note, disgaea_infinite should imply disgaea.

We don't imply studios to their works.

So, is the whole point of the tag just to have a wiki page? As is, it's a pretty worthless tag for searching (roughly even split of disgaea pictures that have it tagged and that don't have it tagged).

EDIT: Apologies for not having seen previous forum stuff about studio implications; I barely spend any time on the forums. It'd probably be helpful if http://danbooru.me/help/tag_implications had some information about this (and any other general types of implications that might have been decided against in the past).

Laethiel said:
As is, it's a pretty worthless tag for searching

You got it.

We have yet to firmly decide what to do with studio tags.

I thought that in general, studio tags should be added if an image has at least two copyright tags that belong to the same studio.

ashot02 said:
I thought that in general, studio tags should be added if an image has at least two copyright tags that belong to the same studio.

company_connection should be added in that situation as well.

ashot02 said:
I thought that in general, studio tags should be added if an image has at least two copyright tags that belong to the same studio.

EB said:
company_connection should be added in that situation as well.

Yes, this is the appropriate use of studio tags. Use them similarly to how you'd include a seiyuu name in seiyuu_connection.

I'd also say use the studio tag when there's a character present who's associated with the studio as a whole rather than with a specific copyright. For example, asagi_(nippon_ichi), particularly when she's alone and thus not meriting a tag for any of the various games she's appeared in.

It's kinda tricky the way most all of NIS' games take place within a common cosmology. Kinda blurs the line between nippon ichi as a tag for the studio, and as a tag for it as a common setting.

Yeah, Nippon Ichi is a special case. I don't think applying the Nintendo tag to every pic of Mario would be particularly useful, but in this case it feels a bit different, since there's sort of a Nippon-Ichi-universe.