This type of fanfiction is so idiotic. Either you watched the anime or read the LN upside down because if you read the Official Source Material, which you should, especially since I see you writing about characters and arcs that are set after the anime ended.
If you read the Light Novel, you would know:
1. No, Rias didn't have Koneko tail him. That's completely anime original. Rias and her peerage don't make an appearance at all in the LN before Issei died.
2. Rias's familiar gave him a pamphlet because he was seen as a potential customer. He was just one of many who got that pamphlet from Rias's familiar. If it wasn't hers, it could have also been Kiba's, Akeno's, or Koneko's familiar.
3. Rias didn't have an eye on him personally. She eventually noticed that a Fallen Angel was in her territory and was doing things, and took a look at that, but Issei himself was completely irrelevant to any of that.
4. She didn't know what Raynere was trying to do. She didn't know Issei had a valuable Sacred Gear, and they had been "dating," which in this case means walking to and from school, for a few days at most before the first actual date and Issei's death.
So, why would she just randomly get involved with that Fallen Angel before knowing what is going on, possibly provoking a battle in which her servants could get hurt, to warn a stranger that maybe possibly might be in danger?
For all she knows at that point, Raynare could just be having some fun playing around with some humans, and there would be no reason for any conflict.
Plus, don't be acting like Issei wouldn't become a devil if Rias approached him and said, "You can get a harem" or something.
YOU ARE READING
The book Of Bullshit Issei Tropes
FanfictionThis book is made to call out bullshit tropes aimed at characters just to change the main ship or give my boy Issei some trauma for no reason.