Movie Pamphlet

I'm reading the interview with Takahiro in the pamphlet and he says that while there were no Vertex attacks in the 300 years between NoWaYu and WaSuYu, there were some major incidents. For instance, there were groups of people who were attracted to the strength and might of the Vertex, and so there were battles with these organisations. There may come a time we get to see this story.

He also mentions the Akamine House, and says their background setting is written out and developed, although currently unrevealed.

Interview from the movie pamphlet about KuMeYu and possible future stories:

Q: Between the Christian Era described in "Nogi Wakaba" and "Washio Sumi's chapter" there are roughly 300 years of blank space, was Shikoku at peace during these times?
Takahiro: There were no large-scale Vertex invasions, but some other major incidents. The memories of the Vertex were still vivid for the people of these times, and exactly for that reason people who admired their power emerged. Conflicts with such groups arose during this long history. We might shed some light on this part of the story one day.
Q: The new "Yuusha de aru" story "Kusunoki Mebuki is a Hero" has launched in Dengeki G's Magazine. What kind of story is it?
Takahiro: [Usual stuff about S1/S2 connection, chosen/not chosen girls, girls called to Gold Tower]
Maeda: Personally, I'm looking forward to when we'll get back to that title.
Takahiro: That's right, their duty isn't to be heroes but sentinels. I also think it's a work that becomes more entertaining the more you know about other parts of the series. I'd especially like the people who watched "Washio Sumi's Chapter" to give it a look. The reason being that a girl from Shinju-kan will make her appearance, and Sumi will be featured through her.
Akashiro: It's also a story that connects Gin's and Karin's characters.
Takahiro: Yeah. The protagonist is a girl who fought over the position as a hero and Gin's terminal with Karin and lost to her. As such, you'll be able to see Karin's past self, and Yuuna and the others will make an appearance in an episode where one of the characters tries to spy on the Hero Club.
source: https://discord.com/channels/204077054608670720/204078471687831552/334294122133192706 (/r/YuYuYu)