Two years have passed since Cloud defeated Sephiroth. He's sick with Geostigma, he is "about to break" as Aerith later explains. In the beginning of Advent Children/Complete, Cloud has rejected the company of his former companions, including his best friend Tifa. He has distanced himself from everyone and has actually moved into Aerith's church. He is seen listening to his voice mails, but not making any attempt to call anyone back. It soon becomes very clear that Cloud and Tifa's relationship continues to be quite strained, as shown in the official novella Case of Tifa.
  
As it turns out, Cloud has been afflicted with a terminal disease called Geostigma. Rather than spending his final days with his family and friends, Cloud chooses to seek refuge in Aerith’s church and tells no one that he is living there. Cloud has refused to tell anyone of his sickness, or to speak to anyone about the deep burden of sorrow and guilt that he carries in his heart for the death of Aerith. Tifa, meanwhile, is running the new and improved Seventh Heaven in Edge, just outside of Midgar. She is taking care of Barret's daughter, Marlene, as well as an orphan boy named Denzel, whom Cloud found one day at Aerith's church. Tifa is also acting as a relay for Cloud’s delivery service by letting him know about orders by voicemail.  


As the movie progresses, it becomes increasingly clear that Tifa is very concerned and even frustrated with Cloud and there friendship becomes strained. He has been worrying everyone by running off to live in Aerith’s church without telling Tifa where he was going, not telling her he has Geostigma, Cloud is away from the Seventh Heaven all of the time, never checking in, never answering Tifa’s calls to his mobile phone, and refusing to speak of his inner issues with Tifa. Tifa's official profile from Advent Children/Complete even states that she is "disappointed in Cloud, who has closed off his heart and is lost in memories of his past", not that he can be blamed for it since Cloud is racked with guilt over Zack and Aerith's deaths. Since there is little she can do, she tries to be a helpful friend from afar while trying to be understanding and supportive. Tifa tries to continue Cloud to let her and their other friends in saying, "You hate being alone, so let people in. Sure you don't answer the phone, but I don't see you throwing it away either.", followed by the scene where the voice-messages from Tifa, Reeve, Barret and Yuffie are being played while Cloud's phone sinks into the water. That scene alone is all the proof needed to support that although Cloud is living in solitude and loneliness, the voices of his friends give him some comfort and company.

At the same time, Cloud is slowly dying. The Geostigma causes his arm horrible pain, and causes terrible memories to come flashing back into his mind. I think that Cloud, at that moment, thinks that if he can be forgiven by Aerith and Zack, and if all of that guilt can just go away completely before the inevitable, then he can die in peace and have no regrets. He won't be causing Tifa and his family any trouble, the world will be better off without him since he can't help people anymore, he would be forgiven, the only way out is being killed by Geostigma and finally resting in peace.


Cloud's grief slowly lessens due to the actions and support of Tifa and Aerith. Tifa treats him as any best friend would despite her frustration with his acceptance of Geostigma and tries to encourage him to fight it at their home, but it is only when he sees Aerith's spirit in the flowerfield and she asks him "You want to be forgiven? By who?" that Cloud finally starts to feel "lighter".  When Aerith discovers that he wants to be forgiven more then anything, she laughs it off. She never truly blamed him for what happened to her, she states later on that he came after her when she ran off, and that was all that really mattered.

Cloud, at that moment, is very stunned and surprised by her response that he turns to face her... only to wake up from his "dream state". The flowerfield vanishes and turns into the Sleeping Forest, and the silver haired men are attacking him. Later on, when he is reunited with Vincent and Marlene, she directly asks what Tifa has tried to tell him:

"Why don't you ever pay any attention to us?" Us referring to Tifa, Marlene, Denzel, and Barret Cloud's family.

Cloud begins to think back to the moment not too long ago when he was with Tifa. She tells him that Denzel is fighting off the Geostigma, and the fact that there isn't a cure isn't stopping him from trying. She yells at him and says to stop running away from everything, and to think about the present rather then the past. She tells him to let people in, not to shut everyone out. And then when they are alone, she finally asks him, "Cloud, which is it? A memory or us?" Once again, us referring to not only Tifa, Marlene, Barret and Denzel, but Cloud as well. The entire family. Memory referring to the people he lost to Sephiroth: Zack and Aerith.

When Cloud silently adds to himself, "But... I let her die...", that is when he hears Aerith's voice again.

"Isn't it time you did the forgiving?"

I think that is when Cloud really begins to believe that the people he loves are suffering because of something futile. All this time he was stuck in the past, wanting to be forgiven for something that he was never blamed or shunned for. He looks up at Marlene and tells her "Let's go home", and the two walk away, hand in hand. Aerith's words were all he needed. She needed to wake him up and tell him that he's hurting his family, he's hurting himself, and that's something she doesn't want to see her beloved do because of her


Cloud takes Marlene home, and eventually reunites with Tifa and Denzel when Bahamut attacks. He tells Tifa that he feels "lighter" now, no doubt because all of that guilt that weighed down on him had finally gone away. At that, Tifa smiles, relieved to see that Cloud has finally came to his senses. Denzel asks Cloud if he'll come home after all of the fighting is over, and Cloud smiles and nods. Denzel's face lights up, and then he rushes back to the 7th Heaven, where he waits with Marlene for Cloud and Tifa to return home.


Now the scene in the church (after that very awesome tunnel scene) is still a mystery to me. I know that the water was indeed "holy water", seeing that the water is in the church, churches are holy, and that Aerith had to summon Holy in order to save the planet), but how it just arrived out of nowhere with no real explanation took me by surprise. One thing is certain, she once again summoned the holy water, had it flood her church, and cure Cloud of his Geostigma (while at the same time, chasing off Kadaj). Aerith knew that Cloud needed all of his strength for the upcoming battle and there was no way that Cloud could defeat Kadaj if Geostigma was wearing him down and destroying him.

The water falls on Cloud's arm. The Geostigma vanishes. And as the last drop of water hits the pool in the church, we hear Aerith voice again: "Let's go, Cloud...". And he goes off into battle.

Throughout the battle, Cloud fights Kadaj and eventually battles Sephiroth as well. We find out from Marlene that Aerith is watching over the fight, and the children. When Sephiroth stabs Cloud with the Masamune and asks him what was the most important thing to Cloud (so he could have the pleasure of taking it away from him), that's when images of Aerith show, and then Tifa, Marlene, Denzel, and the family of friends show. The way I look at it, Aerith was the very important person to Cloud but Tifa, Marlene and Denzel, his family of friends, are still alive. They can be taken from Cloud.

 Aerith was trying to tell Cloud. If Cloud continued to grieve over the people who were no longer with him, there might be a chance that the people who were with him could be taken away from him as well. She did not want Cloud to distance himself from his family and continue to push himself away from them to the point that, when the time comes and something horrible happened to them, he would once again always regret it. I think that's what Cloud realizes in that moment. He does not want to relive all of that grief. He knows what he has to do. He realizes just how precious his family is to him, how precious life is to him...

How precious his friends, and people who loved him, were to him.

That gives him the power to pull the Masamune out of his shoulder, use Omnislash and defeat Sephiroth. And once the battle is over, Sephiroth turns back into Kadaj, who collapses into Cloud's arms. I personally don't believe that Cloud heard Aerith speaking to Kadaj, but I think he knew what Kadaj was referring to when he said "Is it Mother...?". And I know that when the rain had come, and Kadaj was reaching to the sky and his fingers looked as if they were holding onto someone's hand, someone who was lifting Kadaj into the air and making him vanish, Cloud knew exactly who Kadaj was seeing.

I think at that moment, Cloud really begins to feel the weight being lifted off of his shoulders. Everything begins to fall into place. The rain heals the sick children, the silver haired men are gone forever, and he stands up with his head leaned back, his eyes closed, with the rain falling on his face as the Shera draws near. Completely free...

...Until Yazoo shoots him in the back. Cloud is unconscious, his body's floating around, he's on the brink of death once again... and that's when a soft, pale hand is placed on his forehead. In his sleep, he whimpers "Mother...?", which causes Aerith to laugh again. First Kadaj, and then Cloud  everybody starts calling her 'Mother'.

Which is why Cloud wakes up in the church, surrounded by the children Aerith had saved (and who probably saved him, since he was in water and they all seemed to be lifting him out of it). The little girl with the moogle doll tells Cloud that "she" said that if they came to "her" church, Cloud would be waiting. So you could say that Aerith told the children to find Cloud in the church, who in turn told Tifa and everybody on the Shera where he was, and went rushing to aid him. Once again, Aerith saves Cloud and Tifa very touchingly senses Aerith's presence gives her heartfelt thanks.

The end of the movie was absolutely wonderful. It really touched your heart. Everything from Denzel being cured, the children and Final Fantasy VII cast jumping and laughing, Cloud happy with all his friends including Tifa, and the children, and the music just really brought the movie to a wonderful ending. When Cloud looks up and sees Aerith, talking to the children he watches her with wide eyed astonishment and love, as she stands up and slowly walks towards the door, where Zack is waiting.

Cloud watches on, almost unable to believe at what he is seeing. When Aerith tells him that everything is alright now and Zack waves goodbye to his friend, and the two walk away. Cloud watches them leave... and then he smiles. He once again realizes that he is not alone anymore because Aerith will never leave his heart and will always love and watch over him.

To sum it up, the relationship between Cloud and Tifa in Advent Children wasn't a romantic one in the least. Tifa acted like a mother to Cloud. She spoke to him, gave him advice, made him realize certain things and set him straight with Aerith's help. She has always acted with caring and concern to the man she loves through she has accepted he will be eternally in love with Aerith.