Hello! I don't know if op who submitted the asked to you about anzu lore & engirls is going to elaborate, but I want to drop my two cents too since I do like Anzu and find Engirls so interested. I'm sorry if I'm repeating anything you already know and I'm not an engirls expert either so i could be wrong about some of these.

Since you mentioned Engirls Protag and the war, here's the timeline that I believe under the common assumption that EG takes place alongside ES!! (given that Suzu and the bunch, who graduates in the end of EG was Anzu's old classmates and friends)

Anzu is a year older than her little step-brother (protag of Engirls who most fans seems to call Tenn(kousei-kun)). Basically in Anzu's 1st year of high school, she attended Kimisaki Academy, and Tenn was in his last year of middle school. Anzu and the Troublemakers' failed revolution occurred then (supported by the fact that Azusa was a second year in middle school during Paradise), and she suffers from bullying until she decides to transfer to Yumenosaki during her second year. By then, Tenn is in his first year, attending Yumenosaki as well.

In ! Era Anzu has told one of the characters (I forgot who) that her brother doesn't want to be associated with her when they are on campus and to pretend that they don't know each other (but he's at least nice enough to help her promote Trickstar to his fellow general course peers for her during DDD). Generally they have a somewhat strained relationship, which was surmised by various ES and EG characters as teen angst + his inferiority complex with his sister.

By !! Era, Anzu is in her third year, and Kimisaki Academy have decided to go co-ed, leading Tenn to transfer there (don't remember if there are actual reasons stated in-game or if he's just dropped there with no explanation). Due to that, Tenn was able to help the students of Kimisaki, mend their relationships, help Anzu reconnect with her old friends, and talk more with his sister. Anzu actually gets mentioned quite often in EnGirls, like how she makes his bento lunch, Seira sneaking into Yumenosaki to see her, drives her friend Natsumi to school, and etc.

Unlike Anzu who is an only-girl in Yumenosaki's idol course because she's a last minute decided test subject for the producer course (either her or her family most likely agreed out of desperation to be able to transfer), Tenn seems like he's the only-boy in Kimisaki just because he's the only one who enrolled?

There's lot of parts that are implied but still lies in the realm of headcanon/speculation. Like how EnGirls makes it clear that the reason Anzu transferred was due to the bullying she received as the target for the actions of the Troublemakers, since she was always a slacker who the teachers already disliked, but in the EnStars novels she says it's because of family circumstance. Although in the same novel, she (and Chizuru in the novel extra Crosstalk) does give a nod to the events of Paradise, regretting leaving her friends behind and running away; meaning that for Anzu transferring was not because of the bullying, but her own cowardice (although the bullying was pretty bad it was school-wide). For Tenn, the step-siblings have always been described as close growing up, but they have seem to have grown distant lately. Apparently, Tenn had even lived away from their family for a while. One could speculate that maybe he transferred out of Yumenosaki and into Kimisaki (both schools are in the same neighborhood) to get away from his sister, who at that point have probably gained notoriety as a the sole producer of the academy. Given that some stories make it a theme to validate Tenn, and tell him that he's a different person to his sister who is also great and deserves his own happiness, supports this in my opinion.

I'm sorry if this is so long, I hope it isn't rude or anything, it's just that many people have made me aware of how interesting Anzu's character, backstory and current arcs are and I wanted to share that to anyone else that might be interested too. She's pretty complex and well-written if you cherry pick all the stuff about her specifically from the stories, which is why I can understand why many fans consider her as her own character and more than a self-insert.

NO THIS ISN'T RUDE AT ALL, ANON!!! I am literally shaking your hand, thanking you. I'm a little curious as WHAT the Kimisaki revolution was right now....and what part Anzu played.

But STARS I LOVE THIS SO MUCH. You don't understand how much I love this....Anzu predates the Enstars games, firstly (cause I heard engirls was released first). The thing about her being a legacy of engirls, haunting its narrative (at least it seems that her shadow is cast over the engirls era pretty widely), and then switching to a viewer and casting her shadow on the Enstars boys??

I was so wrong in my post about her except also not because her self-insert-ness still feels somewhat significant. Except she's like...a very strange bridge between the player and the characters, existing in both worlds (her and her brother, it seems).

Anyway, Anzu lore is SO cool and I'll have to reread this again to fully appreciate it because man, I love this!