"Well, I guess that's that, then?" Dan asked.
Kat grinned. "Erm, not quite," she giggled. Dan was about to ask what she meant when he felt another wave of changes begin.
Dan felt a pressure build in his chest, and he pulled off his shirt to see what was going on. As he watched, the skin underneath his furred-over nipples expanded, filling with fat, until Dan posessed a perfectly-formed, modest-sized pair of breasts. "Oh no..." he muttered, as he shrank slightly, stopping at about 4'8". As he yanked his pants off, he could see his hips expand as his waist narrowed, his entire body reshaping, becoming curvy, until he was left with a pleasantly curvy but not ridiculous figure.
"Please, Kat, don't do this!" Dan yelped, as his voice became higher and smoother, his formerly short brown hair spilling down past his shoulders, until it was nearly waist-length. But Kat only kept smiling as Dan pulled his underwear off to watch the final change. As his boxers dropped to the floor, Dan could see his privates shrinking, becoming smaller and smaller, until eventually they vanished into his body, leaving her fully female.
Dan stared at Kat. "Wh-why did you d-do this?" she whispered.
"Oh, didn't I tell you?" Kat giggled. "One of the little-known facts about familiars is that they have to be the same sex as the magic-user they support. But cheer up, will ya? It could be a lot worse. Aunt Janice thought I shouldn't even let you be anthropomorphic. Besides, I asked Mom, and she assured me that you'll get used to it. Now c'mon, Danielle, we need to get some suitable clothes on you!"