Hey, this is nice! I really like the dynamic between Tanner and Kaito. In this mission, you really show off their strengths and weaknesses, with Tanner being extremely focused on book smarts and information, at the expense of knowing how to react to people or having much practical sense in general. Meanwhile, Kaito is full of wisdom about survival and avoiding confrontation, but is mistrustful and opportunistic, and has little familiarity with specialized equipment. They're going to be perfect partners to play off of each other, and I look forward to seeing them learn from each other and develop over time.

These "gamer protagonist" fics are real annoying and weird, so I'm glad we've tackled our first now. You made good use of the gamey elements to further harass your agents. I especially liked that they were blocked from portaling around boring parts due to the need for the game to load the next chapters, as well as the health bar that ruined the assassination attempt. But I also like that you turned it against the Harry replacement in the end, by calling him out like a rude player over live chat to get him angry and lose his focus.

The gag of everyone laughing in Medical is definitely funny, but also kind of contradictory, since the doctor did say she would ask Upstairs to leave Kaito alone for a few days while he healed. Unless you meant to imply Kaito was expecting further vacation time after his arm was better?

The List of Errors Part:
There are a few lines where you end dialogue with a period rather than a comma, even though they're followed by dialogue tags:

"'Yeah, basically.' Kaito’s partner continued."

"'You’d be surprised.' Kaito muttered."

"'Kaito, the Stu unlocked Wandless and Nonverbal magic skills, and they’re already at level 25.' he whined parodically."

And then in this line, I think you wanted "Harry's screen" rather than "Jeff's" since Jeff isn't gaming.

"He saw Jeff introducing Harry to a female police officer, Melody, whose stats were once again listed on Jeff’s screen."

And in this line:

"After ensuring everything was in place, he closed the satchel and walked outside his room to watch his partner hurriedly finish putting everything in the backpack and putting it on."

"Putting" should be "put" because it needs to follow the verb tense of "finish". They're both being listed as things Kaito watches Tanner do. (You could also change "finish" to "finishing" instead to make them match, but I think "finish" and "put" sound better.

And lastly, I just want to point out that the LeFay inheritance Harry gains is probably a reference to Morgan LeFay, the enchantress/faerie who lures Merlin away from helping King Arthur.

—doctorlit

I especially liked the bit in the opening, where Kaito meets Tanner. It's a very nice establishment of the contrast between the two.