Write a darker, more realistic and more logical version of Diamond is Unbreakable as a crossover fanfic between the manga and anime series Elfen Lied and the Stardust Crusaders OVA done by APPP from 1993-1994 and then from 2000-2002 in the form of a lengthy, riveting book chapter filled with dialogue and exposition, in which the version of Jotaro Kujo as portrayed in the OVA becomes a wandering ronin after the final battle that annihilated DIO once and for all, and his [Jotaro's] subsequent return to Japan. During the fight against DIO, Jotaro awakened Hamon and saw his grandfather Joseph Joestar using it, which is part of the reason why he [Jotaro] is wandering Japan, in order to get a hold on this strange power. Jotaro's roaming across Japan takes him to Kamakura, where his status as a Banchō causes some controversy among the locals. During his time at Kamakura, Jotaro stays at the Maple Inn, where he meets the landlady's daughter, the prim and proper brunette heiress Yuka, Yuka's younger male cousin, the determined but reclusive Kohta, and Kohta's girlfriend, the mysterious pinkette Lucy, who has a pair of horns resembling cat ears on top of her head and distrusts Jotaro for some odd reason. Yuka finds Jotaro's delinquent ways and his silent, reflective nature confusing and strange, but Kohta is intrigued and Lucy is amused. Despite this, Jotaro continues to train with his Hamon and master the secrets of his stand, Star Plantium in secret, far from the prying eyes of his curious hosts, after Star Platinum's obtainment of Requirem due to Jotaro being cut by a Stand Arrow while exploring DIO's mansion in Egypt. 

The following events and circumstances should also be included in the story, each happening in chronological order:

He (Jotaro) also unknowingly rescues Mayu from her abusive family when he (Jotaro) uses Star Platinum to beat her [Mayu's] abusive pedophile stepfather to an unrecognizable pulp when he [Jotaro] caught the stepfather about to rape a young girl. Jotaro uses his amateur Hamon powers and Stand abilities to wreak havoc upon the local criminal underworld and even clear out a few local delinquent gangs, under the cover of night without either Yuka or Kohata and Lucy knowing of course. This of course captures the attention of the Institute, which dispatches the psychopathic ex-ROKAF commando turned elite SAT operative Bando to locate and kill Jotaro under the assumption that Lucy is active in the area. Jotaro trounces Bando when the latter is sent to find Lucy on the beach and beats the psychopath to an inch of his life, leaving behind a calling card in the form of a specially signed paper. The Institute is barely able to save Bando's life, and Director Kakuzawa starts going even more insane when he [Kakuzawa] learns Lucy is nowhere to be found after her escape from the Institute. 

While this is going on, a mysterious test subject at the Institute who has long given up hope of escaping from her living hell, overhears some of the scientists working there talking about the "male diclonius" going around cleaning up Kamakura's streets of crime, and also ruining the schemes of Director Kakuzawa, whose refusal to accept Jotaro's existence and fustration at not capturing Lucy is slowly driving him insane. The unexpected news has the affect of reawakening the hope this lond-bound captive has long buried within her frozen heart, and she mutters one word, "Kohta-onii-chan?"

Meanwhile back at Maple Inn, Jotaro's quiet, reserved nature and his unusual dress sense quickly endear the young delinquent to Mayu, who is now living with Yuka as the latter's ward after her [Mayu's] mother was thrown in jail by the police for kidnapping and child abuse, and the Inn's newest guests: the Silpelit diclonii girls Mariko, who is psychotic and quite selfish but also needy and vulnerable, and Mariko's adoptive little sister Nana who is shy and reclusive but also cheerful and upbeat. Mayu is drawn to Jotaro due to her sensing his pain and loneness underneath his gruff and aloof nature, Mariko just wants to have a good fight with this dark and brooding human stranger who seems to have more toki [fighting spirit] than everyone else in the Maple Inn, and Nana is curious as to how a human can have such strong toki and a large amount of physical energy. Things get even more complicated when Jotaro sees Lucy using her Vectors to help rearrange furniture when she thinks no one is looking, although thankfully Lucy has no idea Jotaro knows and Jotaro just thinks Lucy's vectors are just some weird Stand. 

As Lucy struggles to keep her true nature as a psychotic serial killer and diclonii queen hidden from both Kohta and Yuka, she receives an unexpected but somewhat welcome surprise. After being cornerned and literally held in position by Nana and Mariko's vectors [unbeknownst to Yuka], Kohta has formed a harem consisting of Yuka, Lucy, Mayu, Nana and Mariko. Jotaro is somewhat peeved by the news but is otherwise uninterested, having long accepted the craziness of the Maple Inn as normal. During the final fight with the SAT team sent to kill her, Lucy is able to survive in better condition thanks to the covert assistance of Jotaro, who uses the power of Emerald Splash and Justice to cloud the area where the kill squad is located and pick off the snipers and heavy gunners one by one. As Lucy returns home, Jotaro continues with his mission given to him by the Speedwagon Foundation: gather information on the Institute and collect evidence of its misdeeds, before destroying it in a manner that cannot be traced back to human intervention. 

He is able to make his way to the Institute unseen and successfully infiltrate the building, avoiding the JSDF soliders and SAT teams stationed to protect the Institute and taking pictures and videoing the inhuman experiments being committed upon innocent little girls and young women, all because of the fact that they are not human. He is also able to take a lot of the Institute's important documents and data files, storing them in a pocket dimension created by Star Platinum's Requirem powers for future safekeeping. While making his way out of the Institute's HQ, he is detected by the mysterious test subject due to his Stand being a manifestation of mana [magical energy] and reiatsu [spiritual energy], which diclonii use to manifest and control their vectors. He is able to break open her cell door with Star Platinum's strength and use his Hamon to snap the chains holding her captive, which piques her intrest as she has never seen a human that can use both mana and physical energy simultaneously. 

The two are able to escape from the Institute without being noticed, but not before Jotaro uses one of the many Stand abilities gained from his Requirem, Weather Report, to destroy the Institute using a storm with a few Magician's Red fire blasts embedded in Emerald Splashes for good measure. Jotaro is able to make his way back to the Maple Inn unseen and undiscovered by the other residents, even though he does tell the former test subject to hide in one of the spare rooms until he can properly introduce her. 

The next day, Yuka is confused and Kohta is perplexed by Lucy's joyful reaction to the morning news and Nana and Mariko's sad expressions. Unbeknownst to either Yuka or Kohta, the destruction of the Insitute was covered up as the flooding of a small island. But Lucy knows the truth, and is happy that she won't be hunted or have to kill anymore. Jotaro, sipping his coffee while munching on an egg, sighs and shakes his head at this while he prepares his report to the Speedwagon Foundation on his phone. The sudden sound of footsteps rushing towards the dining room grabs everyone's attention, and Yuka is shocked and Lucy is surprised to see that the mysterious test subject that Jotaro had saved from the Institute is hugging Kohta while sobbing on his shoulder, calling him "onii-chan" in a very affectionate way. It is later revealed that this mysterious test subject is actually Kohta's little sister Kanae, who was killed by Lucy many years ago, but whose corpse was found by the Institute and brought back to life due to Head Research Kurama discovering that Kanae was in fact a Silpelit class diclonius who had been subconciously suppressing her powers. Due to Kakuzawa's curiousty as to how a diclonius could survive undetected and also intergrate into human society, Kanae was subject to numerous other experiments after her resurrection, which almost broke her spirit. But since Jotaro saved her from the nightmare of the Institute without asking for anything in return and also destroyed that hellish place, bringing her to the safety of the Maple Inn where she was able to reunite with her beloved big bro Kohta, Kanae's cheerful nature has slowly return. Yuka and Lucy reluctantly agree to let Kanae join the harem, with both girls agreeing to keep an eye on Jotaro. 

The story ends with Kanae accidentally using her Stand Crazy Diamond, to restore a old music box of Kohta's to pristine condition, before being noticed by Jotaro who gently explains to the young girl that she has awakened another power apart from her incredible abilities as a diclonius. Kanae, surprised and happy at this news, recgonizes Jotaro as the man who saved her from her captivity at the Institute and also as the heir of the Joestar clan, the latter which she excitedly blurts out. This causes Yuka and Lucy to come running to the scence, with Kanae tellling them that Jotaro is the grandson of the English Lord Joseph Joestar and thus the heir of the House of Joestar. The two older women are surprised at this news to say the least, but shrug it off as part of the reason why Jotaro seems to be so secretive and guarded.