With things coming to a head between the radical and conservative factions, it’s time for Kiriha and the others to take a stance. After discovering a cataclysmic weapon in the hands of the radicals that stands to threaten both the surface and the underground, can they act in time to prevent tragedy? The clock is ticking, but it won’t be the only thing working against them since the radical faction has a little... outside help... on their side.

Just starting high school, Koutarou is moving out on his own to take some of the burden off of his widower father. Lucky for him, he's found a room at Corona House. It has a great landlord, it's not too far from school, and best of all, it's dirt cheap. It really is perfect... except for the strange girls that keep appearing to try and take it over! But even as room 106 turns into a battlefield, Koutarou isn't willing to give up his apartment without a good fight. The invasion begins!

Deciding they need a bit of a break, Koutarou takes the girls out for a day of beetle hunting. An unexpected reunion, however, leads Kiriha to realize there’s more than just beetles in the mountains outside of Kisshouharukaze City. It seems the radical faction has been working in the shadows all this time, and they’ve already established a foothold on the surface. But a factory? Magicians? Automated weapons? It sounds like they’re preparing for something big, but this is only the beginning.

Koutarou and the girls prepare to chase Ralgwin back to Forthorthe, but one critical mission remains before they can leave Earth behind again—they must oversee the welcome ceremony for the next wave of intergalactic transfer students. Little do they know that someone is watching their every move from the shadows, someone with a keen interest in both Koutarou’s sword and Nalfa... Indeed, the Gray Knight is getting dangerously close the group and the truth about what happened back in the ruins. Will their rematch with him be their final showdown?

After getting back from Forthorthe, everyone was hoping they could spend their days in peace for a change. But as if the politics of the official Forthorthian invasion weren’t enough, something very strange and very unsettling is starting to happen around Koutarou and the girls. One mysterious disappearance becomes two, and there’s no clear cause or end in sight. Can they figure out what’s going on in time, or will Koutarou end up just like he was in the beginning—alone?

Now that the invaders have come to an understanding of sorts, things are going smoother than ever in room 106. Spring is in the air--tulips, friendships, and potential romances are all about to burst into full bloom. Koutarou and the invading girls have never been happier together, but nothing lasts forever. Things turn dark quickly when they find out that they're going to have to say goodbye to one of their own... and soon. Without even any time to prepare, will the bonds they all share be enough to pull them through?

Harumi has a special favor to ask Yurika concerning Koutarou, but Yurika will have her own set of relationship problems when a new transfer student shows up at school the next day. The new girl--Aika Maki--is an acquaintance of hers, but she's not the old cosplay friend everyone seems to think she is. If what Yurika says is true, Maki is the evil magical girl that she's been trying to warn the others about all along. The biggest danger now may be that no one believes her.

It’s been two full years since Koutarou first started at Harukaze High as a freshman and a battle for his apartment turned his life upside down. A lot has changed since then. His former rivals are now his closest friends, and they’ve even added a few new faces to the group. Revisiting things like the inter-club obstacle marathon during the sports festival as third-years is going to be a wild ride, compounded even further by the danger lurking just around the corner...

Koutarou and the others have at last defeated and captured Ralgwin, the leader of Vandarion’s faction. Given his importance to the rebellion and Fasta’s threats, however, Forthorthe is convinced it’s only a matter of time before his allies stage a jailbreak. They put everything on the line to keep him in custody. Even the court magicians and the princesses are getting involved, which complicates things for Grevanas. The old wizard grows desperate and finally decides to make his move. With neither side willing to back down, a grand battle lies ahead.

Koutarou and Clan are working their way back home from their interstellar adventure, but they have to make a pit stop about ten years off from their intended destination. As luck would have it, they encounter a young girl right after they land. Worried that she might have seen their spaceship in action, Koutarou decides to dig a little deeper. Things take an unexpected and heart-wrenching turn, however, when he realizes he has more in common with this girl than he initially thought.