Illusions
If there was one thing that could get a person, whether human or demon, killed, it was forgetting that Kurama was first and foremost a thief. He wasn't just a thief: he was an Extremely Good thief. The difference was phenomenal. For to be considered good at something that nearly everyone did, you had to stand out.
Even in his human form, Kurama had the mind of someone who was waiting to pull off a great heist. He was always observing, taking careful mental notes, deciding what could help him escape if need be. Anything that could be used to his advantage was catalogued permanently in the never ending vault of his mind. This made him a deadly opponent before one even took notice of the plants he weilded. Kurama had plans on top of plans and then backup plans for all those plans. There was no move you could make that he hadn't accounted for.
Hiei understood this completely. It was why he always thought twice whenever he got curious about fighting the fox. For all his speed and agility, Kurama would be miles ahead. He also knew, however, that the control freak nature of the redhead usually only extended to fights or contests that Kurama wanted to win. Emotions were usually left out of the careful planning, because Kurama didn't think they needed to be planned for.
He showed everyone what they wanted to see. For Kuwabara, he was the friend he could go to for advice on how to fight, and how to deal with the fact that Hiei seemed oddly displeased with how close he was to Yukina. For Yusuke, he was a beacon of motivation. The former detective longed to be as comfortable being a demon in human skin as Kurama always appeared to be. For his mother, he was the dutiful son. He never stayed out too late, or had wild parties while she was gone. In fact the only visitor he had that was unknown to her was Hiei, and he had no interest in alerting the human woman to his presence. To the rest of Nigenkai, he was a kind young man with an extraordinarily large intellect.
Hiei often wondered if he was just better at reading the fox because he knew his true nature, of if Kurama consciously let more things slip as time passed. The puzzle that was Kurama became increasingly clear to the little half breed, and he wanted desperately to call him on it. But fear won out. He never forgot that the redhead was a master thief, and he didn't know if he could stand to find out that he only knew the fox as well as he thought, because said fox allowed and willed it so.
He did not want to be just another person that Kurama pretended for.