Probably going to take some time to get akunaki blog to provide a brief guide.
Also, is there a skill point cap or are we allowed to max all the classes?
Kunoichi requires the 'Super kunoichi' to be 'registered'. Does she have a phone number? I think there are endings for her.
Also, how does 1 corrupt the girl for lewder state CGs? Is it only via Phone messages?
Akunaki isn't the only JP blog online that reviews and walkthroughs JP doujin games.
I've found another site with the list of endings, but it doesn't have detailed instructions on how to get there. There are enough broad hints available to pursue each ending, though I need to confirm the information myself before I think it's safe to share.
No skill point cap, on NG+ the first round on the train is done at base level. Once the protagonist reaches the school, all points acquired through level-up can be redistributed. After 2-3 runs players should have enough to max out all four skill trees.
DLC character doesn't need the phone number since her ending conditions are apparently tied to her body sensitivity and specific rape scenes executed.
The social media posts are tied to the endings, so players who can't read or don't bother with the correct choices won't get very far trying to get the character's true end. For the lewd end, it should be enough to rape them senseless until they enjoy the experience which is then reflected in their social media posts, a specific number of scenes is required as a prerequisite which is easily checked during the intervals.
Confirmed by the Ci-En: Money in this game is only used to temporarily boost the protagonist's follower count in his social media profile and as monetary compensation if he's caught in the act. Followers have two purposes: they act as a multiplier for currency earned as a benefit from posting pictures of the most recent train trip (the longer and lewder the actions the better) and they increase the chance of followers being on the same carriage as the protagonist which reduces the number of lines to deal with during the interactive scenes.