YMMV / Showa & Vampire

• Angst? What Angst?: Even after being kidnapped at young ages, being tortured and turned into cyborgs, made to kill a lot of people, and even getting killed around a year prior to the start of the story, the renegade NUMBERS have no trouble adjusting to the new environments. Although the only ones who come closer to Wangst are Daichi and Hana.
• Designated Hero: Let's be up front about this, Shinichi and his friends are the cause of the problems in this story. Their presence is what draws GIN-SHOCKER forces to the school (also resulting in GIN-SHOCKER discovering the existence of youkai, leading to them capturing monsters to harvest their DNA and make the kaijin soldiers more powerful), but they never tell anybody despite knowing everything, because if anybody found out they'd lose the chance to go to high school. And despite knowing that a huge evil organization is out there gathering power and destroying lives, they're not very interested in getting off campus and doing anything about it. Toward the end, it seriously becomes a Once per Episode event where one of the heroes wishes GIN-SHOCKER would just leave them alone. The last chapter ends with them going back to Youkai Academy to start their next year, suggesting not much would've changed if the story had continued.
• Fashion-Victim Villain: Chapter 55 starts off on a meeting between all the GIN-SHOCKER branch chiefs, and some of them are described as wearing outfits that would look extremely gaudy and haphazard if actually drawn out, even for anime supervillains. It doesn't really help that the chapter starts on that, but goes on to tackle the issue of suicide.
• Fridge Logic: So you start with Rosario + Vampire, a series about a secret monster world whose members are taught to avoid exposing their true nature to humanity to avoid starting wars. Then you combine it with Kamen Rider, which is all about armored heroes fighting and destroying monsters bent on the destruction of humanity. Shouldn't Kamen Riders be the very symbol of monsters' fear of humanity? It's never mentioned, and the Kamen Riders are idolized by the monsters they meet.
• Iron Woobie: After seeing what Shinichi has suffered and yet bounced back from, albeit by repressing nearly all memory of it ever happening to him, it's plausible that he is this, as he's not The Stoic nor is he a Jerkass or an Omnicidal Maniac driven by his suffering to end the world... even if BLACK 13 has the potential to become the last one.
• Moral Event Horizon: Seeing what was done to Shinichi to transform him into BLACK 13 is enough to convince the unlucky viewers that Dr. Gebok — and GIN-SHOCKER — crossed this in a big way.
  • Ishigami/Madame Medusa also crossed this by way of forcefully converting Shinichi's past enemies into cyborgs.
• Romantic Plot Tumor: The story starts out with the promise of adventure and an intricate series mythology, but after summer break starts and the other main riders are introduced, their social lives and acquiring more members for their harems take over the story. The fights with GIN-SHOCKER are mostly just interruptions.
• Squick:
  • Shinichi's relationship with Yukari Sendou. Rosario + Vampire dealt with that by Tsukune only being interested in Moka (it provides the page image for Unwanted Harem for a reason), and Yukari's dreams of a three-way marriage weren't going to happen. This fic expanded it to Shinichi being in serious romantic relationships with all the girls, though, including the twelve-year-old.
  • After returning from summer vacation, Yuji gets hired as a teacher at Youkai Academy, and his teenage girlfriends enroll as students. Meaning he's banging three, and later more, girls in his class. A later chapter has Leon consider that he could actually "arrest" them for this, but he decides to let them go. Seemingly because they're main characters.