Well, perhaps it could be about Harry being injured in a battle and coughing up blood. Maybe he's in a fight with a dark wizard and gets seriously hurt.
In this fanfiction, it could be that Harry is exposed to some dark magic that affects his lungs. He starts coughing blood and this is the start of a long journey for him to recover. His friends Hermione and Ron would then be on a quest to find a cure for him. They might search through old magic books in Hogwarts library or seek the help of some wise magical creatures.
It could be Voldemort. He might have cast a new spell on Harry that makes him cough blood as part of his ongoing attempts to defeat Harry.
One idea could be that the blood test is a school project at Hogwarts. Students are required to do a detailed analysis of their own blood magic. Hermione would be super - excited and dig deep into research. Harry might be a bit worried as his blood has some unique connections to Voldemort. Ron, on the other hand, could discover something unexpected about his Weasley bloodline that has been lost in history.
It might be a story where a wizard or witch is a huge Shiba fan and during a routine blood test in the Hogwarts hospital wing, they discover that their love for Shibas is somehow encoded in their blood. This could lead to all sorts of adventures, like finding a secret Shiba - filled magical realm accessible only to those with this 'Shiba - in - the - blood' trait.
One possible plot could be that Harry discovers an ancient spell or prophecy that requires him to bathe in dragon blood to gain the power to defeat an even greater evil than Voldemort. So he embarks on a dangerous quest to find a dragon and obtain its blood.
It could involve Harry Potter taking a stand against a dark wizarding family that has wronged his loved ones. Maybe they've targeted his friends or family, and he decides that a blood feud is the only way to deal with their ongoing threats and attacks.
One interesting plot could be Harry Potter arriving at Camp Half - Blood and being mistaken for a demigod at first. He then has to prove his own magical abilities which are different from the demigods'. As he stays, he starts to learn about the Greek gods and their ways, and he tries to find a way to combine his Hogwarts magic with the powers and knowledge at the camp. Maybe he could even help the demigods in a battle using his unique spells.
Well, one possible plot could be that Harry discovers his Saiyan blood during a particularly dangerous encounter at Hogwarts. Maybe when facing a powerful dark wizard, his Saiyan powers suddenly emerge, giving him super strength and speed that he didn't know he had before. This newfound power could change the way he approaches his battles and his role in the wizarding world.
The plot could start with a mysterious portal opening between the two worlds. A Hogwarts student might accidentally stumble through it into the world of Strike the Blood. This would lead to a series of adventures as they try to find their way back home. Along the way, they could meet the characters from Strike the Blood and learn about their world. The student could also introduce some basic magic concepts to them. As news of this strange visitor spreads, it could attract the attention of both the good and bad forces in the Strike the Blood world, creating a lot of tension and action.
The plot could involve a mystery surrounding this person with the blood of the four houses. They could be hunted by dark forces who want to use their special blood for evil purposes. At the same time, they are trying to uncover secrets about their heritage within the four houses.
One possible plot could be that in a world where the magical realm of Harry Potter intersects with the vampire - filled world of True Blood, Godric, being an ancient and powerful vampire, could have some sort of connection to the wizarding world. Maybe he was once involved in a magical pact that now resurfaces. Harry Potter, with his sense of justice and adventure, gets caught up in this mystery and has to work with Godric to either save the wizarding world from a new threat related to vampire - wizard relations or to uncover a long - lost truth about the origins of magic and vampirism.