Tiara's relationship with Fang starts out sour, but grows to be one of reliability and possibly even romance.
Initially disgusted with Fang's mannerisms (albiet, her Tsunderemasochistic tendencies make her enjoy being insulted by Fang) she looks down on him and Eryn, viewing them more as peons to help her gather furies, versus reliable allies. After meeting Harley and journeying to Shukesoo's tower, Fang finally displays his reliability to the group by single-handily defeating most of the guardians on his own. It impresses Tiara enough to remark that Fang is not "Entirely Useless". In the second timeline, after initially feeling insecure about Fang being a "stalker" due to not knowing him at the time, Tiara eventually grew a lot closer to Fang, though she still teases and scolds him from time to time, much like Eryn does. In both the original and renewed timelines, Tiara struggles to accept and comprehend the feelings she has for Fang.
Along with Eryn, the two seemed to idolize Sherman because of his kind nature. It is hinted that the two get along so well with their similar interests (reading literature, distastes over insects specifically cockroaches, world peace, etc). While it was being implied he was forcing the ring/himself onto her, it appears that Tiara still cares about him enough to confide in him that her head hurts (Evil Goddess Route).
In one of her subevents in the Evil Goddess route, she states that she can't bring herself to hate him no matter what corrupt deeds he does, implying she forgave him back in the first timeline.
The only route where she actually does hate him is the Goddess Route where he's the main antagonist.
Tiara distrusts Galdo at first, believing he`s a spy and that Fang is too naive to trust him so easily. It is only after Galdo takes a blow aimed at her from the assassin Ethel that Tiara realizes how wrong she was and properly apologizes to him for being so suspicious of him.