After Sasori's previous Akatsuki partner died, Itachi, Kisame, and Sasori were sent to recruit Deidara into Akatsuki. When Deidara refused, Itachi engaged him in combat and managed to corner him using Mangekyou Sharingan. Deidara was initially impressed by Itachi's eyes, thinking them to be true art. However, he inwardly berated himself afterward, repulsed that he could think of anyone's art to be better than his own.
Though Itachi and Deidara get little panel-time together throughout Part II, Deidara makes references about Itachi and his Sharingan several times and is revealed to admire him. However, he is still bitter about Itachi's "art" being better than him and has trained his left eye simply to counter it.
When fighting Sasuke with C4 later, Deidara reveals that he had been saving that technique in order to kill Itachi. When hearing of the bomber's death, Itachi remains silent and his eyes go downcast. However, the latter may have been a response to hearing that Sasuke died as well.
- Despite his obvious resentment, Deidara is revealed to admire Itachi as well.
Among the Fans
Though not an overly popular pairing overall, ItaDei is fairly popular among Akatsuki pairings. Fans likely support it due to the tense nature of their relationship as well as for aesthetic reasons.