Shin Megami Tensei is a franchise with a lot of spin-offs. Right now the only tags that imply the main SMT tag are the games that have Shin Megami Tensei in their titles (including Shin Megami Tensei Devil Children, which should not in fact be titled SMT).
The question is if we should imply all these spin-offs to the main SMT tag. Right now there are several images tagged as Devil Summoner or Devil Survivor without an SMT tag, so an implication would bring them all together.
The biggest issue would be the Persona, a spin-off that grew so big that it overshadowed the original and gained a life of its own. If we imply it then most SMT posts would suddenly be Persona posts, so maybe it should be excluded?
On a related note, the Megami Tensei tag is useless. Its only possible utility would be to tag the NES games (which were called Megami Tensei without the Shin), but only a handful of posts do that, and it's otherwise redundant with Shin Megami Tensei.