Tifa's anatomy isnt quite as rediculous as you may think, she's just a clever dresser. The belly button should be under the belt/skirt. Her top cuts just shortly after her bust ends, showing her upper abs. The skirt goes from above the belly button, to just (srsly just) below her buttocks, giving the illusion of super long legs and a short upper body. this kind of hides her hips a bit, and can make modeling the hip/waist area kind of awkward.