Just realized that Speed and Black’s relationship is extremely similar to the relationship between Azuki and Coconut from Nekopara (I don’t suggest watching that unless you are at least a teenager)
Okay, I think I know what you're saying. correct me if I'm wrong.
So you're implying Hitachi wishes towards the death of "Humans", correct? Meaning the rule only works for Humans. If a human dies and you want to wish them back, you CAN. But only if its been under a year since they died.
If you want to wish a "Pokémon" Back, its the opposite way around. You can only wish them back, if you're okay with the fact that they have to die again in a year. If this works for "Pokémon" then your right, but Speed didn't want to do that. He wanted to Revive Black's, and i shall quote: "ONLY RELATIVE" because Speed already has some of *his family*. Black had nobody.
Again I may be wrong...
Q & A that he hasn’t seen any mythical Pokemon/jirachi for 2 years, and black recently saw frost in the museum. If it was the rule you just described, black wouldn’t have seen him because if it was the rule you think, than frost would have already died.