Goku's powers are on a completely different level compared to most characters in Highschool DxD. His Saiyan abilities like Super Saiyan transformations give him incredible strength, speed, and energy projection. In contrast, the characters in Highschool DxD mainly rely on magic and their devil or angelic powers which, while powerful, are not on the same scale as Goku's in terms of raw power. For example, Goku could easily defeat most low - level devils with a single punch in his base form.
Issei would be very likely. Since Issei is the main character in DxD, his curiosity and his own pursuit of power would make him interested in Goku. They could train together and learn from each other's abilities. Also, Rias would interact with Goku. As a powerful devil, she would be intrigued by Goku's power and his different way of approaching battles.
Yes, there are some great ones. You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'Goku Highschool DxD' and you'll find a variety of stories with different plotlines and interpretations.
Well, there are several common themes. First, there's the clash of cultures. Goku comes from a very different background than the characters in Highschool DxD, so how they interact and understand each other is a big part of many stories. Then there's the theme of self - discovery. Goku might discover new aspects of his powers or his personality while in this new world. Additionally, the idea of protecting the new world he's in is also quite common. Since he has a heroic nature, he would likely want to keep the Highschool DxD world safe from any threats, whether they're new to him or familiar from his own universe.
Goku's powers in a High School DxD fanfiction would be a game - changer. His ki attacks could be on a level that could potentially destroy entire areas in the DxD universe. His martial arts skills are also top - notch. In a fight, he would use his speed and agility to dodge attacks and then counter with his powerful punches and kicks. His transformation abilities, like Super Saiyan, would be a shock to the characters in DxD. They might not have any means to counter such a huge boost in power.
A possible plot could be that Android 18 gets injured during a fight and Goku takes it upon himself to protect and heal her. This close proximity leads to the development of feelings, which is where the 'lemon' part might come in. Their relationship could be a secret at first as they are from different 'worlds' in a sense, with Goku being a Saiyan hero and Android 18 being an android once created for destruction.
One possible plot could be that Goku is somehow transported to the DxD universe. He might initially be confused by the different rules and magic there. Then, he could start training with the devils and angels, sharing his own fighting techniques. This could lead to some epic battles where he combines his Saiyan powers with the unique abilities in the DxD world.
A 'dxd lemon fanfic' is likely to be a work of fan - created fiction related to a 'dxd' property. Since 'lemon' in the fanfic world often indicates some form of sexual or at least highly romantic content (although not always), it might be centered around the characters of 'dxd' engaging in relationships that are more intense or physical. However, different authors can take this in various directions, from exploring unrequited love with a bit of a steamy undertone to full - on romantic or sexual encounters between the characters, all while being set within the 'dxd' world.
Lemon fanfictions, in general, often involve sexual or inappropriate content which is not suitable for all audiences. In the case of Goku and Bulma, it would be a very unorthodox take on their relationship as in the original series they have a platonic relationship. Such fanfictions would deviate greatly from the original tone and values of the Dragon Ball franchise.
I'm not sure if there is an existing 'goku and wonder woman lemon fanfic'. Fanfics can cover a wide range of pairings, but this particular one might be quite rare or not commonly known. It also depends on the specific fanfic communities and platforms you search on.