Welp, picked this up because of a combination of "it got a reply recently so it popped up in my notifications" and "Hey, it has nice looking art"... and ugh, I'm honestly disappointed... and that's with my expectations being pretty low to begin with. Honestly, this game is bad... and to an extent, I don't know where to even start with it...
I suppose I should start with the translation quality, which is pretty bad. It's one of Saikey's weaker releases even by their pretty low standards... so keep that in mind if you end up playing it. It's almost certainly either poorly edited MTL, or done by someone with a relatively weak grasp of the English language. Regardless of how it was done, it's pretty clear that the game didn't get a proper proof-reading pass because some of the mistakes in there are obvious even when a sentence is taken completely out of context. All in all, the fact that they're asking money for this garbage translation should be a literal crime tbh.
Luckily, the translation, while aneurysm inducing, is still clear enough that you can get what type of game it is. This is a game from the "McCuck-kun is a retard that gets settled with an absurd debt, and his (would be) significant other ends up dealing with lewds because of his idiocy" category. The whole debt or whatever thing isn't a bad idea in and of itself, but this particular sub-category of using that trope requires the people involved to be utter morons more often than not, and it results in a sub-par story. This is especially the case here, where MC is such an utterly complete dumbass that plenty of people will likely want to see him cucked.
The whole thing hinges on the bull provoking MC into a duel... which MC didn't have to accept at all, and which he knew he couldn't win. He'd literally just seen the guy fight with his would-be GF a couple of days earlier, being one of the people able to get her to fight seriously... while MC struggles fighting f'n slimes... It's so utterly stupid that it honestly takes the cake for the most stupid set-up of this type that I've ever seen. (Or at least, if there was a set-up that was dumber than this one, it was either in a comedic game or I forgot about it.) What comes after that is equally stupid and non-sensical, but the end result is that the MC has a debt to repay, and during this time, Aiel, the would-be GF has to do "special training" with the bull, Karl, who of course uses the excuse to mess with her sexually.
Now, the shitty story and equally shitty world-building (which barely exists anyway) would've been tolerable, if there was anything else of quality of in this game... Sadly, this isn't the case. The gameplay that follows involves MC diving into a dungeon to slay monsters and make money and all that jazz. To further hobble the player, the MC has a very limited set of actions that they can take per day. They can only fight 5 times per day (for some reason) and they're weak as fuck (they struggle with slimes, as mentioned before). However, they're helped by their powerful sister, who can, of course, only act twice per day, eats up one of MC's action points anyway (for some reason), but who can one-shot any monster and guarantee a kill.
Assuming you care enough to repay the debt before too much happens to the would be GF aside from some molestation, it's pretty obvious that what you need to do is bum-rush through every level to the top of the dungeon (it's apparently a tower) and maximize the profit from Yuni's ability to murderize the toughest of the tough. There's three treasure chests you can pick up too for some money, 2 with low funds around the slime levels and one at the very top that gives 20k. Combined with a couple of Demon or whatever kills from the last 2 floors via Yuni, you can easily have ~35k gold by the end of the 1st day. The total debt is 100k btw. In any case, this wouldn't be so bad if the game was actually designed in a way to turn this bum-rushing into actual gameplay... Sadly, it's not. The map designs are obnoxious. The monsters have eyes in the back of their head and are all fairly fast. Their movements are completely random. Their chase range is pretty long. They can also engage with MC and consume one of his action points just by touching him.
All in all, it's tedious to deal with and doesn't rely much on brain power to beat, but on pure luck and patience. However, if you do everything right, you can repay the debt before Aiel gets forced into much aside from some molestation and maybe a blowjob.
Doing this gets you the so called Happy Ending, where MC and Aiel just talk together on a cliff and you'll probably regret that these two complete morons don't jump off said cliff to spare that world of the propagation of their genes. No. They don't get together in the ending. Also, said ending includes Karl vowing to keep trying to fuck Aiel. Yuni isn't mentioned at all even though she clearly has the hots for her big brother (I'm not buying that they're not related... It feels like that was edited in tbh).
Regardless of how you do things, if you want to get this ending, Day 10 is the latest you can wait until paying the debt (this is entirely doable btw, just a pain in the ass to pull off). Why? Because on Day 11, Karl finally fucks Aiel for the 1st time, and for some reason, the second his dick is in her, the game is set to the second ending, the "Aiel becomes Karl's bitch in secret and starts thinking the MC is a loser for no reason" ending. I honestly have no idea if this is intended or not. I say this because, if you follow the events that happen every couple of nights, Aiel isn't corrupted after the first time she gets Karl's dick in her, and it takes, uh... 2 more scenes I think? In any case, that ending probably shouldn't be locked in until at least Day 15-16, probably even later, but eh...
As is, the progression of events from "I hate Karl" to "OHMGeee Cock shooo ghud!" is so fast that your head will likely spin. Same with Aiel's progression from "I'll do anything to keep McCuck-kun safe" to "I'll humiliate this total loser to get dicked harder!". Basically, if you're looing for any kind of proper corruption progression, don't bother with this game, it's not worth the effort.
I wouldn't recommend it for "mystery NTR" either, because you literally don't see anything from MC's perspective until the very end. No Karl and Aiel fucking just out of sight. No her opening the door/curtains while being fucked behind it. No sprites of them fucking around through the overly large academy. No nothing really. There's no sense of mystery, just wasting time until the day where he conveniently gets to see them fucking.
Yuni's progression is even worse, amazingly. She isn't involved at all until MC sees Aiel getting fucked by Karl (at which point he has a mental breakdown like a total bitch), which leads to Yuni finding Karl and Aiel fucking, and getting pulled into bed and fucked. You could say raped... but she got horny over that dick from the moment she saw Aiel screaming like an animal as she was skewered on that fuck-pole... A couple of fuck-sessions and days later, and she's all aboard the "I'm a total slut for Karl's massive cock" train without even trying anything with McCuck-kun, in spite of the fact that up until that point she was shown to be quite obsessed with him. This leads to the 3rd ending of "Karl gets both bitches and fuckes them in front of MC, and they're totally ok with it as well as treating him like garbage". I get it that they were trying to say that Yuni was a closet nympho from the get go (her ero-stats page has her starting at 4 star lewdness, out of five, and with a 1000-something masturbation count showing that this girl is perpetually horny...) but they made no effort with the whole thing at all.
They could have at least tried to have her seduce the MC, him failing to please her, and then her jumping on the Karl train... but nope, too lazy for that fam.
On top of everything else, H-scenes are nothing particularly special either. They're not bad. Definitely usable and all that, but nothing to really write home about either. Granted, the crappy translation lowers one's ability to fully enjoy them.
All in all, my recommendation is that if you DO pick up this game (and I hope you didn't pay for this shit, because Saikey doesn't deserve a single dime for the crap they did here), just go in and out of the dungeon repeatedly and trigger the events until the 3rd ending. It's not worth engaging with the poor excuse for gameplay, and it's not worth trying to get the 1st two endings the legitimate way. They'll both be unlocked in the gallery anyway, and you don't need to do anything special to see the ero-stats update every day. Skip the two quests in the game, including the one about helping Yuni, and just treat this as a shitty kinetic novel in RPGM about some dude getting two hoes addicted to his dick. You waste a lot less time with it.
Honestly, to an extent, I regret the fact that I bothered making an effort with this crap... though that's mostly because, shitty writing aside, the idea itself does have potential if used properly. It's just... NOT used properly, at all.