Anji's position in the tier has been slightly debated in AC.
Some people think he's the worst character in the game. Others just think he's bad without being the worst. Regardless, the spectrum is in the C-D range for tier.
I honestly think he's a solid C tier character. Decent damage off of combos, great reversal options (like GP's and Fuujin), butterfly makes for great okizeme, plus one of only 2 characters that has 5 guts (and at 106% damage, he's pretty blessed on the side of defense). Problems he faces are that his mixup isn't amazing, all of his Fuujin followups are horribly unsafe on block, butterfly has a humongous recovery period, most combos are reliant on having 25% tension (at least to get good damage), and he's not terribly great at taking control of the field like say Venom, Eddie, or Testament.
I happen to like him simply because he is amazingly versatile. No matter what situation you are put in, there's always an option open to you as long as you are willing to take some risks.