Where Every Scroll is a New Adventure
The reason why this question comes up is because Fukuchi is built up very heavily, as an incredible fighter and as a big boy villain. In comparison, Aya is a self described incredibly average girl with no special traits. So the question goes, how did Aya outsmart Fukuchi?
1. Fukuchi isn’t actually built up to be smart. Fukuchi is strong as hell, he is the perfect soldier, he can take down armies, he is Fukuzawa’s equal or greater. But he has never won because he was particularly clever. He wins because he has the overpowered weapons, the element of surprise, and a very good ability (+hunting dogs surgeries). This is not to undermine his overwhelming combat prowess but he is just a little stupid! Do not be fooled by his confusing time shenanigans! This man is more himbo than you think.
You can skip to the next reason but I don’t want to sound like I’m making unbased claims so here is why I think he’s (as stated) a little stoop:
In his first ‘battle’ we see he almost frees his own prisoner, his second battle he wins because of time shenanigans (where at the end he is outsmarted, if by chance), he mistakes a tracking device for a flash drive, he didn’t foresee being found out by Ranpo despite knowing the ADA, he is bested by his own subordinate in battle and again only wins because of time shenanigans, this is a small one but he literally monologues his plan! Bitch what if that tracking device was also a recorder!! Old man doesn’t understand technology. His own subordinate who he expected to betray him gets a hit on his neck, and even after beating said subordinate he didn’t even know then that there was anyone else was in the room, and etc.
2. The encounter of outsmarting was very short, probably under a minute in between Fukuchi finding out someone was in the room, and Fukuchi being called away. I have no doubt that if there were any more time Aya would be dead, but great luck was on her side, very simply.
3. If during his whole fight with Jouno he didn’t realize Aya was there, then him not realizing Aya was in the coffin isn’t that unlikely. Especially since the sound of breathing and rustling would just sound like Bram. Even with the heightened hunting dog senses he isn’t Jouno, he can’t parse different heartbeats.
4. This ties into the first, but he is used to high combat situations. He is not used to these types of encounters (he has subordinates for the grunt work of killing witnesses) so non-head on fights would catch him by surprise. Aya’s moves are so simple that that is what claims her victory in the end.
All of these are theoretical but I find Fukuchi’s constant running into small evil plan inconveniences situation to be hilarious, which is beautiful because it’s even more surprising then that he’s actually the closest to taking over the world and doing the most damage any character ever has. Fukuchi as a villain is Fyodors opposite, where Fyodor has the all encompassing vibe of having everything planned out, Fukuchi has small issues constantly stopping him. While Fyodor commands total respect from his subordinates, 3/4 of Fukuchi’s have gone against his plan in some way (two directly betraying him). Where Fyodor killed nobody noteworthy, Fukuchi has killed 3 well established strong characters. Fukuchi being bested by a 10 year old is the biggest highlight of their differences: where Fyodor’s plans are a graceful sword slash, Fukuchi’s plans are a bashing mallet.