Mind you, and this is only optional. Take this story ark/ideas with a grain of salt.

I was wondering if Robin can be converted to a Dark Kight.

At night, Robin goes to a location where the Dark Knights spawn. He encounters a Dark Knight, but this Knight is different. It had not only a glowing Moon and Sword crest on its chest armor from its aura but also had dark ore studded on the Dark Knight's shoulder pads and gauntlets.

Now, mind you, this only happens if Robin is defeated, and the last action is being fucked by a Top Blue/Versatile Red Aura Dark Knight's cock or sucking cock of the Green Aura Knight (Which is incredibly rare) and cum when reaches Climax. After the defeat, Robin wakes up at home but staggers from getting out of bed and feels something dark coursing through his body. He will have a meter saying how much of this darkness is occupying his soul.

Option #1 Finding a Cure:

There is a way to counteract this. Speak about this situation to Horace at any time at which the dark meter is filled too, and Horace will ask Arthur for a special book that was long lost. Arthur is having trouble finding the book, and with some references that he did manage to find, he might know where the book might be.

From here, a new location will appear on the map. It will be another temple-like structure in the forest. From what Arthur had said, the book is situated at the top of the pyramid on a pedestal that only appears at night. Once Robin tries to get the book, he is confronted by a Dark Knight. If Robin defeats the Dark Knight, Robin obtains the book but is invisible during the day (Dotted outline of a book). Giving the book to Horace, since it is very powerful, it can only be opened and read at night. Horace says it will take several days to find a cure.

Once Horace fully reads about Robin's situation, Horace explains to Robin how he got affected by this. Certain Dark Knights (Black ore studded shoulder pads and gauntlets.) have a special type of cum produced from the Dark energies coursing through their bodies. Once the Dark Knight releases their special cum into any orifice of any normal soldier/man defeated in battle, their soul/aura is converted slowly to the Darkness. These types of Dark Knights are rarely seen in battles and wandering. If confronted, it's best to flee, but if you wish to battle it, you must defeat them at all costs.

Once Horace finds a cure, he will ask you for the ingredients for this cure. Once Horace creates the cure, Horace then tells Robin to find Giant Lloyd and bring him to his brewing basement.

Once Robin can get Lloyd to come at night in Horace's brewing basement, Horace says, like the Dark Knights, the only way for Robin to get rid of this dark sickness is by someone drinking the cure and cumming the concoction into the affected person. Giant Lloyd is the preferred person since he has a similar body and cock size to the Dark Knights. Confused by this, Robin sees Horace giving Giant Lloyd the glowing concoction. Without hesitation, Giant Lloyd starts drinking the cure. The liquid makes Giant Lloyd's aura glow white, accumulating aura energies into the ball sack.

A screen prompt will pull up, saying that Robin has to have Giant Lloyd reach climax. The cure is only one shot. If failed, Robin has to repeat the same process, creating another cure and doing the same procedure again. 

If Lloyd reaches climax, we will see new screen slides of  Giant Lloyd fucking Robin and cumming into Robin. Giant Lloyd's glowing white cum goes into Robin, and Robin's body glows white as the dark aura from inside Robin leaves his body and disappears. Robin kisses Giant Lloyd once Robin is glowing fully white as a thank-you.

By the time it reaches morning, Horace appears again, saying the ritual is a success. With the cure inside Robin, he is immune to the power of the Dark Knight's cum.  Horace says he will bring this breakthrough in defeating the Dark Knights to General Grant/Captan Benton. Robin thanked both Horace and Giant Lloyd for curing him.

 Or an option of not exactly immune, as the cure will become a shield instead. Each time Robin losses to a Dark Knight, the Aura Shield lowers to a certain amount. Once it reaches 0, he is vulnerable to the Dark Knight's dark cum energies.

Option #2 Accept the Darkness:

Once the meter reaches full Darkness, Robin transforms, having his body, muscles, and cock growing bigger, along with a glowing aura covering his eyes. Once fully converted, he is not allowed back to any normal locations on the map (except the Dungeons, to a certain extent). But there will be new locations on the map: small towns and encampments owned by Dark Knights/Dark Entities that have been invisible to the outside world and can never be seen by normal/magical means. Also, Solitude Peak will show on the map if Robin has not reached the end of the campaign yet.

Now fully converted, Robin will meet new characters from the dark side. Some Demons or Dark Knights have their helmets off, and their eye color is still the same as their aura. Also, Robin might meet certain affinities from certain dark characters. When Robin meets Grant X near the portal at Solitude Peak, Grant asks Robin if he wants to join the ranks and conquer Helgem.

If Robert accepts the Darkness and Grant X's offer, dark tentacles start to fly out from the portal behind Grant and wrap around Robin. When the dark tentacles started wrapping around every part of Robin's massive body and every orifice was plugged, black aura energy came out from the portal through the tentacles towards Robin's tentacle-covered body. With a loud cackling noise from the electrified tentacles and Robin releasing cum as he climaxed, Robin's entire body and cock aura grew bigger, thus giving out more pleasure when sparring with an opponent. Also, this darkened aura gives Robin a higher tolerance rate upon reaching climax. 

With this done, the tentacles release Robin until he is on the ground. Then Grant X walks up to Robin and bestows upon him the armor of the Dark Knights.

Now wearing the armor Grant X that was given him, Robin's new mission is to follow Grant X's orders to take over Helgem.  Robin will do some fetch quests and certain missions that will help better establish the Dark Knight's foothold on Helgem. For each completed quest, Robin will go up in the army ranks.

At certain levels, Robin can meet up with the Dark Portal again and have the tentacles add another colored aura to his body. Robin can now switch between Aura's during battle. Robin will have the third aura once he does certain missions for the Dark Portal.

 Robin can still participate in planned attacks and raids from Grant X as an option. If the Dark Knights win, the town/location will lose a certain amount of morals on their meter. If the town wins, the moral meter returns in full. Once the Town's/Location's Moral meter reaches 0, the Dark Knights occupy that town/location.  Thus unlocking previous/new resources for Dark Knight Robin.

Once Robin reaches a certain rank, General Grant X will give the option of Robin of choosing where to attack/raid. All locations on the map, besides Wheelcum, are available since it will be the endgame for this location. Also, there is an affinity for Grant X; his story is dark about how he sided with the dark powers from the portal.

Once all of the Towns/Locations are occupied by Dark Knights on the map, attacking Wheelcum will appear as an option.

Once attacking Wheelcum is available, Robin will act as a spy for the army. Now in the game, Robin was first introduced to Wheelcum and was branded as a member of the town. Robin was accepted easily by hiding his aura, acting as a normal man fleeing the Dark Knight's occupation, and showing his mark from the town. Robin sees the town in a disorderly fashion.  The town is overpopulated with disheveled men/orcs/beasts that have fled from their towns run over by Dark Knights. Robin wasn't concerned about this as he went to the castle. He sees the twins, Tristan and Hector, keeping a large angry crowd at bay from entering the castle. Tristan and Hector heard from General Grant's order to accept Robin into the castle since he is an ally.

Once General Grant/Grant X leads Robin into his empty quarters, both men make love while discussing their plans. The plan was simple, with dark powers from the portal, General Grant/Grant X could open up a portal in his quarters and let the Dark Knights into the castle.

As night falls, General Grant/Grant X opens a portal in his living quarters, and a flood of Dark Knights starts emerging from the portal. The Castle Guards were stunned to see a bunch of Dark Knights racing out of General Grant's quarters. It's the biggest battle orgy between the Dark Knights and the Soldiers of Wheelcum. During the ensuing battle, both Grant X and Robin are confronted by Horace when both try to get to King Tyran. As a last-minute attempt, Grant X pushed Robin into the King's chambers while sealing doors behind him to confront Horace.

Now Dark Knight Robin confronts King Tyran. Robin battles his way through all of the Kings Guards and Servants. Once the Soldiers and Guards are out of commission, King Tyran rises, and Dark Knight Robin starts preparing to battle the King.

If King Tyran wins, he says to Robin he has never felt such pleasure in eons, and Robin becomes the personal servant to the King. But at the same time, King Tyran accepts the darkness in him and covers all Wheelcum with Dark Powers from the Portal.

If Dark Knight Robin wins, Robin takes the crown and sits on the throne. King Tyran, now defeated, is now reduced to becoming a personal servant/slave to King Robin because he never felt such pleasure for eons and begs more of it from King Robin.

Whew, it took me forever to write this. I thought about this a while ago but decided to have the courage to write it.