A true 100% would be something where you have to get auto+ on every craft, max out the friendship with every companion, complete all the bliss quests (which needs streetpass), complete all the other side quests, get each life to creator (which will be the easiest thing but already takes 1d) and potentially collecting every item (which means RNG from the goddess statues). Technically also max level but you will hit that either way.
A true 100% does not make sense as a speedrun, because it would be anything but fast. A casual 100% would be to get all lifes to creator (which is a category we already have), since that means you can accomplish basically everything (altough you could also beat the Trial of Light and complete all the God Requests to proof that you can accomplish everything). Idk if that would be worth it's own category though, since 98% of the runs are identical.