Hello!

You can recruit ninjas by collecting their Fragments up to the required amount that you need. For example, 2 stars ninja needs 50 frags and 3 stars ninja needs 80 fragments. Ninja Fragments are obtainable from Elite Instances and Events. Others are from Treasure Boxes and other parts of the game. Now, for Konan [Taisho] version, she is currently placed as the reward ninja for participating in the event called "Anniversary Fireworks Celebration" event. While Might Gai, the regular version is obtainable from Seal Treasure (via free draws) and Elite Instances, and his Gate of Joy/Shock version is obtainable from Events and from the Power Rewards Interface of the game.

For Fireworks, you can buy boxes of it from the Regular Shop. Click the Shop Icon located at your lower right part of your game screen and go to the Purchase Limit Tab. From there, you will find the Anniversary Fireworks Gift Pack.

But for buying Konan [Taisho]'s fragments directly, as of now, she's not in any events where you can redeem her frags directly. You can only get her from the Anniversary Fireworks Celebration Event by using Fireworks.