The "irrelevant to the plot" reason due to death, disappearance, or whatever is not why (or at least the main reason) TN chooses to exclude x character. This isn't Persona 4 Aren
Look at Ein for example
- He debuted in DoA 2 as a significant character of importance (which is big deal for a male that wasn't even an active ninja yet.) that even was
prominently featured in the box-art of the dreamcast version. The takeaway is he was an amnesiac karate dude trying to find out his identity,
- At the end of DoA 2 his brief role to the plot came to an end once he recovered his memories and ditched his alter ego so he can return to being ninja Hayate starting DoA 3.
- Ein was quickly forgotten in future games in regard to the plot with only reference to his fake existence from Hitomi (who became the 2nd karate specialist character funny enough) that got smitten over him.
- Despite his zero plot relevance past his debut game he has still an unlock-able character for DoA 3, DoA 4, and most recently DoA5U (was omitted from vanilla due to time constraints).
- The reason he stuck around was either because he was an old fan favorite that keeps coming back in every DoA sequel, to give an alternate karate character option to Hitomi, he was easier to make due to Hayate/Hitomi existing, or possibly the rumor about Itagaki being a fan of him was an influencing factor.
If Tengu for example doesn't get added it won't be because of the plot, but more harsher realistic reasons that I won't bother typing out because it will only end up pissing off Tengu fans and things are already hot here already with the amount of emotion being thrown around here.
