This definitely beats most of the VNs posted here. You seemed to be heavily inspired by Higurashi and Umineko - especially Umineko I think - because I believe the style is nearly completely similar. Detective Butler's peculiar habits could be referred to Holmes, although he is obviously a lot more compassionate. However, this is still definitely a good quality VN that deserved a read for its somewhat interesting story and consistent good art/music.
It is not without flaws though. One of the biggest problems I have with your work is the closure. While the twist in the end was sudden, it wasn't exactly described well and I had a hard time understanding the culprit.
The sudden insanity or explosion of malice
simply felt subpar and cheap that I'd rather you not put it in there because ultimately the story definitely could have done without it.
And then there was Butler
predicting that the culprit would run for their car and planting a homemade bomb in the engine.
Let's state what exactly is so wrong about the whole thing. One, what Butler did was basically terrorism and absolutely illegal. He was lucky he did not
kill the culprit with that ridiculous stunt of his, and from the looks of 'engine exploded into flames' 'car swerving completely out of control' he VERY nearly became a murderer himself. It'll make far more sense if he just punctured the tires instead. Two, if we go by your logic he had managed to concoct the chemicals with the stuff Celica brought him, searched and found the car, broke it open and planted the explosive in. That's in my opinion a pretty damn short timing window where absolutely anything could go wrong.
Not even Sherlock Holmes at his time was THAT insane, so to speak.
The ending was the story was unfortunately not satisfying. It ended way too abruptly without explaining properly the various reactions of the related passengers after the mystery was solved. Also, for a state-of-the-art ship when the
boiler room exploded into flames, the fire alarms REALLY should've rung even when we suppose that there are no sprinklers at the place. What's even more mysterious was that no one seemed to give two shits (or not written in the story that they cared) about a freaking fire in the ship and one of the bodyguards shot and possibly dead. Even the protagonist seemed to have forgotten completely about it and just... left the dude to burn in order to chase the culprit.
In short there were various common-sense-errors that were really jarring, all for the sake of creating a compelling drama which, didn't really turn out that great at the end of everything.
In the end it was still a good kinetic novel, and I'd really like to see more in the future. Hopefully by then your writing skills have steadily matured, and we could expect far more and better mysteries to be read and devoured.