The sword phases into the ground, as though it were a pool of water, energy ripples expand out, turning the surrounding area dark, and within seconds, two rows of a thousand giant blades rise up from the ground "Senbonzakura Kageyoshi ( Vibrant Display of a Thousand Cherry Blossoms)"
Seeing the thousand of giant blades magically rising up from the ground, Itachi a slight premonition a what is going to happen, premonition that become true when he hear Ren voice once again "Chire (Scatter)" and so the thousand blade scatter in a uncountable number of flying blades as they move through the air like torrents of waves, they give the appearance of cherry blossoms flowing swiftly along the wind
With a simple hand gesture, Ren sends a huge wave toward Itachi, who choose to charge forwards with his shield ,the Yata Mirror, raised but as the uncountable blades were about to clash with Susanoo, it magically evade Itachi charge and hit him in the side, sending Itachi clashing against the mountain.
Even if Itachi was unhurt by the attack thank to Susanoo outstanding defence, he noticed that his Susanoo was still damaged 'He is really strong, not only genjutsu do not work on him, but now with this many blades not only his attack has improved, but now he can attack and defend at the same time, and I can't use Mangekyo anymore without risking, worsening my condition, already using Susanoo to this level is putting a huge strain'
As Itachi was thinking, Ren move closer to him and noticed the tears of blood coming out of Itachi eyes 'Better end this, I do not know how much time it takes to cure blindness, and I can feel only us here, before coming here I hoped that Zetsu would come and spy on him, what a pity....'
Then Ren says "I'm going to show you that you can at least trust my strength" as Itachi get out of the crater and once again move closer to Ren, "Senkei (Slaughterscape)" and the next moment all the scattered petals unite into complete glowing swords, numbering in the thousands, which form four rows.
These rows float just above each other, and circle around Ren and Itachi in a continuously moving, column-like array, and as Ren raise his hand he says "Now this should prove you that I can help you and Sasuke" and swing it down.
Then from the top row of the array, one sword descend like a missile toward Itachi so fast that even if Itachi can see it with his Sharingan, he can't react to it, the glowing sword then hit Susanoo and pierce right through it, like butter, then hit the ground barely missing Itachi.
Itachi look at the hole in Susanoo then at all the glowing sword surrounding him, then as the Susanoo is fading away he turn off his Sharingan and says "Ok, I'll listen to your plan and then if it is possible, I'll join your group".
Hearing Itachi, Ren nod and undo his Bankai and return Senbonzakura in her sealed form, then he says "Let's go inside, I do not want to talk under the rain, I had enough water, please lead the way"
And so Itachi led Ren into the Uchiha Hideout, in a vast meeting hall which had the symbol of the Uchiha framing the doorway on either side. At the front of the room, elevated above the rest of the room by a platform was a throne of sorts a small table beside it.
This throne has the Uchiha crest on either side of it and two tomoe-like shapes below those as well. Directly behind the seat is a poster which has the kanji kitsune, literally meaning fox, surrounded by eight swirls. The design of the throne itself allowed for the poster to be clearly visible behind it.
The hall itself was in a dilapidated state as there are numerous indentations in the wall, as Itachi sat on the throne Ren thought 'He really like this place' and Itachi as if reading his mind says "This is the only place outside of Konoha where I can still feel some connection with clan, anyway what is this plan of yours?"
Before talking Ren once again checked if they were really alone and once he did so to be more safe he also used the Hachigyō Sōgai (Eight Joined Twin Cliffs) barrier to isolate and conceal them, noticing that Itachi tensed up he says "Do not worry this is a barrier to prevent from begin found, for those outside it is like we are in another dimension, they won't see, hear or sense us"
And next Ren starts explaining "First we let Sasuke train with Orochimaru for another year and half, At that point he will be able to temporary free himself, but we both know that Orochimaru left something in his Cursed Seal, that is one of the reason that guy is so hard to kill, but that is easy to resolve, next he will come after you, and here we change your plan, I will use my illusion on Sasuke to simulate your fight and death..."
But Itachi stops him "Wait, while your illusion is strong, It has still some flaws that he would be able to pick up, like that it doesn't cause damage...." but Ren doesn't wait for him to finish and explain "Like my sword before also my illusion has a second level, so that is not a problem, right now the problem is your illness and your near blindness, but I can for sure cure your Illness as for your eyes I have to try, by the way I didn't finish, after Sasuke "kills" you, we will take him away and tell him the whole truth, and after that ask him to join our group, so what do you think?".
Itachi in a somber tone replies "So your "grand" plan is to use my plan, but without me dying and then tell Sasuke everything? How do you think he will react to that?" and with a smile Ren says "Well from what I know in the 7 year I had with him, he will first get angry for begin fooled, then when he learn your side of the story, he will want to destroy Konoha for what it made you do as he still love you more the he like to admit, but since we will be there and not some masked one-eyed sharingan user that like to manipulate teen something I'm sure he learned from someone else...."
Hearing about the Masked man who Itachi still think is Madara he ask in disbelief "How do you know about him?" and Ren replies "The fourth Mizukage Yagura told us about him when we killed him last year, he was under the Masked Man control, and he also told us that he was together with someone with a cloak with red cloud on it, so I'm pretty sure that he control from the shadow Akatsuki too, that is also why until we free Sasuke, I want you to remain in the Akatsuki as a double agent, just like the old times, only this time, different from Danzo I won't hide anything to you, so what do you think?"
After thinking about everything Itachi finally said "Okay, I'm in" then the first thing Ren did was to heal Itachi of his illness, and then tried restoring also his sight, and luckily he was able to do it, but the whole thing weakened Itachi for more than a month, after that Ren went back to his hideout, and started once again his journey with Peri.