“Arrow” fans have patiently waited this season for Ray Palmer to shrink and complete his transformation into the classic Atom. In “This is Your Sword,” the season’s penultimate episode, Ray doesn’t go subatomic -- although he seems to be conducting an experiment that could finally get us there -- but another classic DC Comics hero does make a long-awaited debut: Katana.

Yes, Tatsu finally appears in full costume, slashing through the League of Assassins as we see the culmination of her tragic love story with Maseo. The moment may take a backseat to Oliver’s rise to Al Sah-Him, but it’s among the most powerful of the season. Maseo thanking his masked wife for killing him and ending his suffering will be long remembered by “Arrow” faithful. But how did we get to such a tragic moment?

Last week, we saw Oliver kidnap Diggle’s wife Lyla and threaten his daughter. It seemed from his actions that Oliver is now beyond redemption. It’s something Diggle has trouble accepting, even as he and Laurel clean up the streets of Starling City. So when Malcolm Merlyn shows up to reveal that Oliver’s Al Sah-Him is a ruse to win Ra’s Al Ghul’s trust, you can imagine Diggle has a difficult time believing him.

However, we witness the truth firsthand, with Oliver and Malcolm plotting against Ra’s in Nanda Parbat. Ironically, the only link Oliver still has to his friends is a man none of them will ever trust. But with the fate of Starling City at stake, this is the only play Oliver has left. Along the way, Ra’s entrusts more and more of his history to Oliver, who’s playing the long game, relying on Malcolm to bring Team Arrow to Nanda Parbat to stop the delivery of the Alpha Omega virus.

We learn from this week’s flashback that there’s no cure for the virus, which killed a large portion of Hong Kong, including Tatsu and Maseo’s child, when it was released by General Shrieve. Tthe death of their son marked the end of Maseo and Tatsu’s loving relationship, with the former drawn into the clutches of Ra’s Al Ghul and the latter sent down the warrior’s path.

Tatsu arrives in Starling City to tell Team Arrow to trust Merlyn. Somehow it works, and she, Diggle, Laurel, Merlyn and Felicity board a private jet to stop Ra’s from dispatching the Alpha Omega virus. With the Atom’s help, they stop the plane, but sadly, Ra’s didn’t put the virus on board. During the battle, an epic confrontation between Tatsu in her awesome gear (seriously, they got it perfect) and Maseo takes place, with Katana besting her estranged husband, finally giving him the release of death. So in the same episode, we’re forced to watch Tatsu hold her dying son and her dying husband. I hope Tatsu sticks around for next season, as she has developed into a powerful presence. And more Rila Fukushima is always a good thing.

With the attack on the plane, Ra’s realizes there’s a traitor in his midst. Oliver is able to blame the newly deceased Maseo, but Ra’s isn’t buying it: He wants Oliver to prove his loyalty by exposing his former friends to the Alpha Omega before his wedding to Nyssa, who, by the way, is having none of this marriage nonsense. The tough-as-nails assassin rebels against her father, even smuggling a knife into the ceremony in an attempt to kill the groom. Oliver is too quick, however, and we end the episode with Team Arrow succumbing to the virus, and Nyssa and Oliver being pronounced husband and wife.

I’m pretty certain “Arrow” didn’t just kill off 80 percent of its cast, but I’m anxious to see how this cliffhanger ending will play out. We know Oliver will appear on “The Flash” this week, to help Barry take on the Reverse-Flash, but it seems as if there’s a long way to go between the wedding chapel of Nanda Parbat and Central City. So how will Laurel, Felicity, Diggle, Tatsu and Ray survive?

Oh, yeah, we also see Thea reunite with Roy before he leaves again, not wanting to draw her into life as a fugitive. However, he gives her the Arsenal suit, so if Oliver and company ever do return from Nanda Parbat, they may find a new Speedy waiting for them.