Some Transformers could be indifferent. They might see fanfiction as something that has little to do with their real missions and existence. Bumblebee is a popular character, but not all Transformers would care about the stories made up about him in fanfiction. They are more focused on their own tasks and the overall well - being of their kind.
One challenge is integrating the two very different universes. The Transformers universe is based on science - fiction concepts like advanced robotics and intergalactic travel, while Highschool DxD is more about the supernatural and a school - based setting. So, making the two fit together seamlessly can be difficult.
The characters in DxD would be quite shocked at first. Ichigo's appearance and his powers are so different from what they are used to. For example, Rias Gremory would probably be intrigued by Ichigo. She might try to form an alliance with him, seeing his potential as a powerful ally. Issei, being the main character in DxD, would likely be both jealous and in awe of Ichigo's abilities, and might challenge him at first but then learn from him over time.
Harry would probably be cautious at first. He's used to strange things in his world, but these giant mechanical beings would be quite different. Hermione would be curious and start asking a million questions about how they work. Ron might be a bit more fearful, especially if the Transformers made loud noises. But overall, they would likely be intrigued and see if they could be allies against any potential threats.
Issei would probably be the first to want to fight Thanos. He's always eager to prove himself and protect his friends. He might initially underestimate Thanos due to his own growing power and confidence, but soon realize how powerful Thanos really is. Rias would be more cautious. She would likely try to gather information about Thanos first and then formulate a plan to either fight or negotiate with him.
Issei, being the hot - blooded character he is, would probably be excited to meet someone as powerful as Naruto. He might challenge Naruto to a friendly spar at first, hoping to learn from him and test his own strength. And as he gets to know Naruto better, he could start to see him as a brother - in - arms, especially if they face common enemies together.
There's also 'Transformers in the DxD World'. In this fanfic, the Transformers characters are introduced into the Highschool DxD setting. The story often focuses on how they interact with the different species in that world, such as the angels, devils, and fallen angels. It has some great action scenes where the power of the Transformers is pitted against the magic and abilities of the DxD characters.
Well, considering that Titans are mindless creatures in most cases, they may not have a very complex reaction. They would likely see the Transformers as large, moving objects and target them as they would any other large target. But if the Transformers were to use their advanced weaponry and abilities, the Titans might be deterred. For example, if a Transformer used a powerful energy blast, it could make the Titans hesitate or retreat. Also, the Transformers' ability to transform might puzzle the Titans and disrupt their normal behavior patterns.
Rias would be devastated. Issei was not only her servant but also someone she had deep feelings for. She would likely go into a rage at first, vowing to find and punish whoever was responsible. Akeno would be heartbroken as well. She and Issei had a special bond, and she would be in mourning for a long time. Kiba might feel a sense of guilt, wondering if he could have done more to protect Issei. Asia would be in shock and constantly pray for Issei's soul, hoping for some kind of miracle.