I think Trails and Tales might be too niche. If people want them done, I'll do them though. But I think Trails should at least be saved until a bit after Chapter 1 comes out this fall, since it'll give more people an opportunity to experience the series.
Mass Effect could be cool.
Pokemon has already been done by someone else. I'd consider doing just each line of pokemon, but I still think that might be too many.
Fire Emblem I think has 600 characters. But you might be able to get it down to 469 if we exclude Heroes from Fire Emblem Heroes. (At least that's what the AI answer is, no clue if it's accurate and I'm too lazy to count)
Also could be in consideration: Mario, Zelda, Resident Evil, Street Fighter, Mortal Kombat, Metal Gear.
The user formerly known as Ashethan