Okay so hear me out on this.
Tikki and Plagg can transform into a human form.
They go to school with Marinette and Adrien occasionally, usually to an event or something, because the get bored being hidden.
When they transform into humans, it is the only time that the two can interact.
I imagine Tikki as a small red head, with blue eyes, (like taller then Alix but shorter then rose height.) and freckles. She is super bubbly, but is pretty poised. She is cute and guys love hitting on her. She always turns them down, mostly because she loves Plagg (Much to Marinette’s confusion)
I imagine Plagg as a tall lanky black haired guy with green eyes, (Like a tad bit taller then Adrien, but not as tall as Kim.) He is lazy and has a shaggy like hunger. When it comes to Tikki he is insanely jealous, he will casually walk up to the guy and tell him to back off. The guy will obviously retaliate, and Plagg’s response is a rather sound beating as he is ‘too lazy to argue ‘. (Adrien is both terrified, confused, and impressed by his Kwami’s skill)