I'm having so many feelings about how the ADA was basically created for Ranpo. to protect him, help him carve a place for himself in a society that shunned him and left him to fend for himself, and it was created by a man who knew him for less than a day, saw a lost, hurt child and decided to take him under his wing.
(Though Ranpo had to pester him into it, I like how he saw an upright, jaded man, a good man, and decided to put his trust in him).
Moreover, Fukuzawa didn't really have a stable job, was drifting around, but decided to help a complete stranger who needed it.
He (unintentionally, and most likely regretted it afterward), gave Ranpo a crutch, something to believe in, helped him to accept himself and the society around him. He literally helped Ranpo to look at the world in a different light. Got a Gifted Ability Permit to create a safe space for Ranpo. Surrounded the other with good people who will accept him and understand.
The entrance exam isn't just to test their capabilities, it's also a sort of litmus test to test their character, to weed out people who will accept Ranpo as well.
It's always interesting to debate when Ranpo 'found out' that he's just a normal person, and I honestly think he always knew, he just didn't want to face it, until the showdown with Poe happened.
Ranpo most likely saw through Fukuzawa's lie from the start: he did say that the glasses were just an ordinary pair of glasses, but he needed something to trust, so he intentionally ignored the truth and believed in the lie instead. (remember, he was just 14 when he was orphaned, and didn't understand why he saw more than others. The people his parents sent him to didn't understand him and shunned him. He was emotionally vulnerable).
And right now, he's watching as all the president built for him chip away and crumble, he's had to face betrayal at the hands of someone Fukuzawa trusted, watch people die out in front of him. He's suddenly thrust into the forefront of this uphill battle, with almost no one to trust
There isn't really a point here other than that I just love these two's found family dynamic and how it all started, I remember how happy I was when I found out that there was an actual light novel written about the founding of the ADA.
(references from Light novel 3 The Untold Origins of the Detective Agency)