Personally I don't enjoy M/F all that much, so I was a bit disappointed with how much of the content it makes up. That said, I do really like this dev's art-style, how they write and "direct" their scenes, and the corruption elements.
Mechanically, this is amongst the best H-games of the year for me, despite it being dead-simple - or perhaps because of it. The gameplay is improved over Shinobi Gear, with corruption and status effects to make it more challenging and strategic, despite still being driven largely by random chance - whilst also tying the H content and gameplay closer together.
This is how you do it - well, one way at least. I've long maintained that the mechanics of H-games of this type (where the player-character is, let's say, not the dominant one) are best when they operate on the same conventions as survival-horror - which can be boiled down to more of a focus on trying to stop numbers from counting down to zero, instead of only making them go up (or never having them really change) as you progress through the content - avoiding lasting negative effects, having limited opportunity to regain any of whatever you lose - level or progression design that has the potential to compound previous failures.
Shout-out to Angel Apostle Liebe for its stamina/HP-management system, as well as the fact one of the two player-characters (who you usually control simultaneously) can be captured if they're beaten on a mission, and you have to solo a smaller side-dungeon as the other. The longer you wait to regen the surviving character's stamina, the more the captured one has to endure. It took a long time (and a lot of mistakes) to reach anything close to a true failure state through that system, and the rescue missions were usually quite easy, so it enabled the player to experience most of the content without it (or the failures required to trigger it) feeling either too punishing, or too inconsequential. And I think Shinobi Train overall strikes the same kind of balance.
The Quarta Knight games by Kudarizaka Guardrail also do a similar thing, but leaning much heavier on status effects than any kind of resource management.
The multiple-choice side-events I found kinda annoying - most of them being towards the middle to end of a level, where you're most likely to have incurred status debuffs and Reason loss, and have to play the timing/guessing game with them. It's an interesting feature and an appropriate way to implement more scenes - but in execution, if you're trying to beat the level, I feel the penalties were a bit too harsh for the progression curve.
I feel like the boss fights (the only traditional battles in the game) could've done with being more engaging and challenging - they're basically a test of whether or not you've maintained enough Reason and Chakra to proceed to the next stage of the level. I'd have suggested a rock-paper-scissors type system - attack/defend/magic-attack for the Player Character, vs the enemy's H-attacks which reduce MP, physical attacks that damage HP and/or incur status effects, and more powerful attacks that need to be defended against or evaded. So you can go through without taking significant damage.
The danger-level mechanic I like quite a lot, it adds a bit of determinism to a game otherwise largely driven by random chance. I think it'd work even better if the actual chance vs danger level were a bit more skewed - eg 40% danger would translate to an actual 30-25% chance.
These are all minor criticisms though. All told, it just makes me more excited and optimistic for whatever they choose to make next.