In this entire series, the party development is directly linked with the route u picked, who u conquered first/fought first and your overall ranking once chapter ends. Basically u gotta conquer the entire map area in a specific number of turns before winning the "main target" that will end the round chapter. The lower amount of turns and more areas u conquer, higher will be ur final score, those final score generate extra items to convert into equipment later, the options will slowly open as u get more and more of these base materials... so u can craft end-game stuff later u need S++ in all Chapters. Cheat Engine to fix turn number and elapse turn value to 1 is ur friend for this.
This is the image for the medal amount with blank down it, the x10 is the conversion ratio to any free medal based in the girl u conquered/chapter u at
Based in the chapter u are/girl u conquered, u free more kinds of units in these menus on the left side in this part
There's also some kinda of intermission stages added between chapters where u meet a situation that u can choose 3 routes, to help(law) or to fight an specific race. The very first one have as the chaos option in the middle to "Attack the Fairies". By beating the fairies and seeing the fairy queen h-scene, u open more of fairy/elves units. These are also spread through the story... if u picked a different route/alignment it would open another race than fairy folk.
Outside of gears, whenever u finish a chapter u also open/release badges, those badges are used to open units, when u conquer a girl, the elemental badges of that girl is freed, basically u have BLANK medals that u can convert into medals from the same element as the girls as u slowly advance the story, using as example the red dragon girl will give u materials to create dragons(medals related to that) where u burn your BLANK medals converting into those. There's a hard limit of how many units u can hold at once(should be around 148) and also better ranks at the end of chapters release more BLANK badges. The phase of the moon/elemental affinity changes the mood and base stats of the units, it's represented by a face in the unit creation screen. Pink face with heart in eyes means the unit will have highest possible growth ratio with using these medals as materials, similar to phase of the moon u can alter the combo of medals pressing on the alter, this will also generate a passive skill/battle ability that unit can use/change their starter mood/growth rate as u level them up. Here's a screen with an unit with best growth ratio+best mood and tactical skill active, if i press on the alter button it'll change the medals used, change it's mood and also remove the tactical battle skill
Every unit have a basic kind like farming, development, etc... they get a fixed value of exp based in how many territorys of such kind u have and ur development level, in the hospital there's a button that exchange to the development value where u can power level ur stuff to 50 so ur units get max bonus exp each turn, even if not used.(Farming will get bonus level based in farming development tier). Here's the screen of the "Internal Affairs"
Its also good to point out that the Chaos/Law value tends to define the ending u're reaching based on ur choices, seeing more scenes/corrupting the girls more will lock u outside of their possible ending or lock the ending where mc is happy with girl X, while having high chaos value and corrupting everyone will throw u into the chaos ending. Both endings outside of the normal where u balance everything and don't pick any have their own special fights, final bosses and corrupted heroines tends to have higher base stats than their normal versions. U can also go for heroine x ending that later should open their special version in a NG+ that is as strong as their corrupted final form(without being corrupted obvious). But with small changes like, more healing than dmg, higher def than atk, etc. If u want the pure love route, choose answers that boost law value, don't see any scene that mc uses hypnosis on the girl/push them further, don't corrupt their advisors. Basically the only scene with tentacles/hypnosis should be the very first/conquest and then, doing the non h-scene events amplifying their friendship value ti'll the end of the game. A combination of all that is what throw u in the law ending + heroine ending based in the one u focused most of ur AP points on the chapter intervals.
You can get all the info u need to know in what kind of route u are in the intermission screen that is like this
It have information on the chapter of the story u are(these games tends to end in like 8 or 9 chapters, 7 tends to be if u don't meet any condition so u don't see any of the true law/chaos ending bosses. It have information on the corruption of the girls(the whip image and number), the number of encounters that the girls themselves liked/talks with them and their affinity(the heart). Down these u have the "Action Points" that limits ur encounters/talks with the girls... Also if u choose like "Sylvia in the Baths"(the corruption scene related one and push further stuff) it'll erase the "Great Minds think alike" where u would talk with Sylvia+Anora, amplify their friendship point by 1 and also, avoid the hentai scene with her and her advisor at this point.