Tiny Race information

The way i read it, and the way the rules are written, players are usually not allowed to enter another creature's space. Hence, the rules in step up saying adjacent because by the base rules, tiny creatures are not a playable race, and thus a non-issue in regards to this feat because npcs usually don't get player feats. Now, granted that to be playing a tiny character, your DM is already allowing something to change the rules a bit, you will have to work around the wordings of certain abilities and feats because tiny creatures do not follow the same rules that most creatures do. If it were my game, I would rule that step up allows a tiny character to remain within the square of their enemy so long as it falls within the rules of the feat, meaning the character cannot take more than a 5 foot step. My reasoning behind this is the feat's purpose is to keep you within reach of the target. For most creatures, being adjacent is still within threat range, but this is not true for tiny creatures since they have a natural reach of 0. Thus, since the intent of the feat is to keep an enemy within reach, I see that a tiny creature should be able to remain within the square of the defender so long as they move within the restrictions of the feat.