After the first chapters, the rest of the story can be continued in whatever way one wishes to write it. However, if one were to ask me for a rough list of things that I think ought to happen, it would be the following (in any order you want, although a few of them I think should have a more specific order):
Touka learning about Lisanna's family - Touka tentatively asking if Mirajane and Elfman will take her to see Lisanna's grave, wishing to pay respects to her friend, which, after a moment of hesitation, agree to. Natsu and Happy wish to come along, and while the Strauss siblings are reluctant at first, they they walk there, Touka asks them questions about how Lisanna was, and while it is a sad subject for them, they inform her of all their happier memories, to which Touka shares some of the kindness Lisanna gave her - once again without telling them she was a Ghoul, although they see that she is indeed hiding something. Touka however is able to pacify their suspicion by denoting they had a bad fight over a misunderstanding, and that while they patched it up right before the end, it was the last in-depth conversation the two ever had, so she feels somewhat guilty that it was the last real time they spoke before they separated regardless of if they made up right as she left, wincing as she privately remembers how Lisanna was taken away without sharing it with the others. Their suspicions offset, Natsu, Happy, Mirajane and Elfman reply that they understand.
The Guild's thoughts about Ghouls - the Fairy Tail mages musings on Touka and what she tells them about Ghouls, debating whether or not what most people think about all Ghouls being monsters could be false. Many of them, including Evergreen, Freed, Brickslow, and Cana think that Touka is a nice enough girl, and would have never suspected her to be a Ghoul. Others like Marco, Wakaba, Bisca and Alzak denote that she could be lying or that she has a darker side to that comes out when she's hungry. Gajeel and Juvia perhaps have the most sympathy to the idea of being treated like monsters and rejected by others, feeling sorry for her. Wendy and Carla cite that they believe her and that, even though she smells of blood, she's honest. However, Erza interjects that even if Touka is good compared to other Ghouls, it doesn't change the fact that they're still a threat, even if they can't help what they are - she admits that he feels sorry for them and, if Touka is being honest, he would like very much to help them, but they still have to stop those Ghouls that kill other people. Gray questions that, if other passive Ghouls are indeed out there, whether or not at least some of them could be convinced or talked down like Touka, which gets most of the guild thinking, and Makarov, upon being questioned on the matter by Erza, ponders what he will do about Touka and if he should even tell the Magic Council that they have her with them.
Bad Habits, Worse Ideas - On the trip to the Graveyard, Touka denotes that she never liked them because of her heightened senses - when they ask what she means, Touka reluctantly explains that the scent of human flesh in the area sometimes makes her hungry, and that she always feels disgusted with herself for thinking such things in the cemetery. After the briefest moment of revulsion, Natsu expresses pity for Touka, denoting that it must be hard living the way she is.
Men in Black - The "Black Runes" make their presence known as they sweep the area, and also interview Natsu, Lucy, Wedny, Erza and Gray regarding their recent encounters with Ghouls, with the group electing to hide Touka's identity as a Ghoul from them. The "Black Runes" questionable methods are also spotlighted, which leaves Fairy Tail struggling to make sense of who is in the right and who isn't.
Expanded Hunting Grounds - Rize and Lisanna attack other Guilds in their trek across Fiore, including Blue Pegasus and Lamina Scale, leaving Lyon and Yuka badly injured during a fight with the two Ghouls. Other Ghouls attack the Guilds as they are motivated from the shadows by the Agori Tree, spurning the beginnings of a dark war.
Wolf in Sheep's Clothing - A new up-and-coming author who appeared as if from thin air, San Takatsuki visits Magnolia one day to explore, and meets Wendy Marvel and Levy McGraden, both of which read her books and find them good if not a bit sad, although Gajeel has actually taken a liking to them. Wendy and Levy befriend San, unaware that she is actually a naturally-born Human-Ghoul Hybrid, a Kakuja and leading member of Agori Tree - the One-Eyed Owl, who also doubles as another member of Agori Tree, Eto.
Hell Hath No Fury - Lisanna makes a habit of trying to hunt down and devour Lucy, especially after discovering how close Lucy is to Natsu and becoming hurt as her own memories of when they were kids drift to the surface, sparking jealousy in Lisanna as her splintered mind and it's two halves - Human and Ghoul - fight on if Natsu replaced her with Lucy. She eventually becomes obsessed with trying to devour Lucy, and eventually it shifts into a vendetta against all of Fairy Tail as Lisanna continues to develop into a Ghoul and becomes more and more merciless as the "Black Runes" try to hunt her down, augmented by Rize's continued influence on her as "the only thing (she) can depend on right now."
Blood-Sisters - Lisanna and Rize's relationship as companions and comrades, and in a twisted sense, friends is highlighted, as Lisanna has become uncaring of others and overtly callous as Rize to strangers, but holds a deep-seated fear of her fellow Guild-Mates.
Preludes - The Agori Tree Dark Guild is encountered a few random times, with some of their members attacking other Guilds, with Levy being attacked and barely avoiding being gilled by one of them.
(This next scene would take place probably partway through, maybe after one or more ghoul encounters - including Levy nearly being killed by a Ghoul)
Symbolic Message: To Mourn Oneself, To Destroy Oneself, and to Remember One's Friends - On another trip to the Cemetery, Touka freezes up and start sniffing the air deeply. This Mirajane, Elfman and Natsu, but she soon explains that it's not because of the bodies, but because there is another Ghoul in the cemetery. Shocked, they ask where, and Touka points straight ahead - which is in the direction of Lisanna's grave. When they arrive, they see a form in a hooded black cloak standing in-between a row of tombstones, among witch is Lisanna which Touka confirms is a Ghoul. Curious and confused, Happy openly wonders why a Ghoul is here, with Elfman worriedly and hesitantly asking if it came to feed on the bodies. Touka grimaces at the insinuation, but admits it's possible. However, the Ghoul instead falls to it's knees and stares at Lisanna's grave for a few moments, making Natsu wonder if it's another Ghoul Lisanna saved.
Then, everyone is left shocked and horrified as the Ghoul suddenly manifests it's Kagune and smashes Lisanna's gravestone to pieces.
Natsu, Mirajane, Elfman, Touka and Happy are all left in states of shock at what the Ghoul has done. However, it quickly turns to horror as the Ghoul openly states - seemingly to nobody - it has been "wanting to do that for a long time" and continues to smash what's left of the headstone. At this point, the horror turns into molten rage as the five observers scream at the Ghoul to stop, all of them attacking at once - with Touka only having the time to make a passing notation of the Beast and Satan Take-Over transformations that Elfman and Mirajane undergo as she screams for the Ghoul to back away from Lisanna. Much to Touka's shock though, the Ghoul acknowledges her, it's eye widening in amazement at the sight of Touka - which gives Happy a shot at the Ghoul, distracting it long enough for Mirajane to smash the Ghoul from behind, allowing Natsu and Elfman to attack and pummel it.
However, the Ghoul shrugs the attacks off and blows them back, fighting them back for a short time before they eventually pull back, staring down the Ghoul. The Ghoul finally looks up at them from beneath it's hood, and Natsu, Happy and Touka are stunned to see that it's the same Ghoul that nearly killed Lucy and Natsu several nights before at the Ghoul Den, recognizing the black mask that only leaves one eye exposed - a Ghoul that Touka recognizes by it's distinctive Kagune as "Chimera," due to the top pair of tentacles looking like wings and the bottom pair looking like two tails. This time, Natsu picks up a scent that is vaguely familiar, but he doesn't piece two and two together, as the Ghoul fights them in what Natsu realizes is a half-hearted manner. However, when Mirajane and Elfman begin cursing the Ghoul as a monster, it suffers a severe reaction, twitching and convulsing as if having a breakdown - a reaction that Natsu recognizes as being the same as when he first fought it, remembering that he had been angry at it for hurting Lucy.
The Ghoul "Chimera," clutching it's skull in the wake of it's episode, then unleashes something that stuns Touka - a Kakuja, which is a unique mutated form of a regular Kagune, only caused when a Ghoul eats other Ghouls, denoting that the "Chimera" is like Rize and the One-Eyed Owl. "Chimera's" Kakuja takes the form of a series of interlocked plates on the shoulders, biceps, back, spine and chest, with a pair of chitin-covered tails and a pair of armored wings that are shaped almost like a raven's. It's face gains a skull-plate with four horns that starts at it's forehead and arcs over it's skull, letting it's silver hair fall free like a mane, while a bony crest grows around it's exposed left eye to act as a form of protection for it, making the Ghoul's appearance even more monstrous-looking and giving credence to it's names of "Chimera" and "One-Eyed Demon." Shocked, the Fairy Tail mages denote that "Chimera" is even more of a monster then they believed if it could eat it's own kind, which sets the Ghoul off, leading to a fierce battle between them all.
Touka is forced to use her own Kagune during the fight, but finds that she cannot pierce the Ghoul's wings, which it folds in front of itself like a shield whenever threatened - but she notes that it does so on instinct rather then conscious choice, making her realize that "Chimera" is an incomplete or half-Kakuja that hasn't finished it's growth, and thus is liable to go into a state of insanity when using this form. Sure enough, it enters a berserk rage and proceeds to injure all of them - even Happy, who is flung through a tombstone like a toy, enraging Natsu further as he tries to attack the Ghoul, only to be pummeled and nearly killed.
Mirajane and Elfman try to fight it off together, but it easily overpowers Elfman and begins to do the same to Mirajane. However, when Elfman tries to get back in the fight, the Ghoul cares multiple wounds into him and forces him out of his Beast Take-Over state. The Ghoul is about to lash out at him, but Mirajane steps in at the last moment - and as a result, is impaled through the stomach by one of the Ghoul's tails. However, this sight actually seems to shock the Ghoul out of it's berserk rage, and it seems to suffer a moment of regret before violently casting the crippled Mirajane onto the floor, with Touka throwing herself in the Ghoul's path, saying she refuses to let Lisanna's sister die.
However, the Ghoul only becomes more enraged at this - but doesn't attack. Instead, it suddenly brings up it's tails and plunges them into the ground, tearing away the dirt and earth until they succeed in hitting something, and with a single swift movement the tails rip Lisanna's casket from the dirt and smash it into another headstone, shattering it's casing and sending the corpse inside sprawling. Everyone is shocked and horrified at this, watching as one of the tails retract from the shattered casket to heft up Lisanna's deteriorating, formally-interred corpse. The Ghoul finally looks up at them again, seeming more calm - then, as if to deliver the final nail in the coffin to them, the Ghoul unseals the mouthpiece on it's mask and bites down into Lisanna's corpse, tearing a large chunk out of the nape of the neck - an event that sends Natsu and Touka into a frenzy, with Mirajane and Elfman forced to watch from their injured states as the Ghoul casts Lisanna's mangled body at their feet, before resealing it's mouthpiece and, of all things, laughing at them in a crazed cackle as if something about the way they treat the corpse was funny to it. Beyond the point of being enraged, both try to get up, but the Ghoul's wings batter them down, and it's tails smack Natsu and Touka aside. Standing victorious, the Kakuja Ghoul leers at Mirajane and for a brief moment seems about to try and eat her, but instead it simply picks up Lisanna's corpse and tosses it in front of her and Elfman, giving one last insane laugh before taking flight and fleeing as it begins to rain.