Implicating collar_to_collar → cobondage
Link to implication

Reason:

By definition, cobondage is a situation where two or more characters are bound together. collar_to_collar is a specific instance of that.

That said, I found some possible counterexamples from collar_to_collar -cobondage, where it's not obviously sexual:
post #1501972 and post #1420945
From the wiki, bondage only applies if it's sexual. The cobondage page doesn't specify.

EDIT: The tag implication collar_to_collar -> cobondage (forum #278780) has been rejected by @NotMeNotYou.

There is also a tied_together tag, which itself seems to apply to both sexual and non-sexual situations (though the wiki description places greater emphasis on sexual situations, for one reason or another).

After a quick glance of the wikis, tied_together and bound seem they could apply to sexual or non-sexual posts, while bondage is for sexual situations. To me, it would be better to implicate collar_to_collar -> tied_together -> bound, however I'm uncertain about what to do with cobondage.

The wiki for cobondage could be edited to specify that it's for sexual situations and then implicate cobondage -> bondage (and possibly implicate cobondage -> tied_together as well), or cobondage could simply be aliased to tied_together.

Yeah cobondage should not be tagged to non sexual images even though it's not especially specified in wiki.

D.D.M. said:
After a quick glance of the wikis, tied_together and bound seem they could apply to sexual or non-sexual posts, while bondage is for sexual situations. To me, it would be better to implicate collar_to_collar -> tied_together -> bound, however I'm uncertain about what to do with cobondage.

The wiki for cobondage could be edited to specify that it's for sexual situations and then implicate cobondage -> bondage (and possibly implicate cobondage -> tied_together as well)

Agreed. Bondage is for more sexual situations. I think that collar_to_collar being implicated to tied_together is a better idea. collar_to_collar should also imply collar as well.

The tag implication collar_to_collar -> cobondage (forum #278780) has been rejected by @NotMeNotYou.