Age of Aincrad will be a free to play game, and will feature in-game micro-transactions using an item shop.
Micro-transactions won't give any in-game advantages to the player. The item shop will include only cosmetic items which will make the players look more appealing to themselves. Other than those cosmetic items, there might be name change items and some other items which will not affect the game in any way, thus the game won't be "Pay to Win".