Sword Art Online's third season kicked off in 2018 with the longest arc of the original light novel series to date, Alicization. Unlike the previous arcs in the series thus far, Alicization was set to be adapted with four cours of episodes before it comes to an end. The first half of the third season came to an end in early 2019, and the third cour of the series brought the War of Underworld arc to its climax. But it's going to be another wait before the War of Underworld comes to an end this Spring.
The fourth cour of the series' third season will be bringing the War of Underworld to its explosive end when Sword Art Online returns this April, and while it's going to be a bit of a wait, the series is stoking fans' flames with a stunning new poster touting the huge developments coming for the major battle between the human and dark territories.
「SAO アリシゼーション War of Underworld」2ndクールのキービジュアルが公開となりました！https://t.co/ZsF6Ht7L9E
最後の望みは、彼に託された――December 28, 2019
Episode 12 of the series brought the third cour of the series to an end, and left things off at a huge cliffhanger. Kirito's still in his coma, Alice is now in the clutches of Gabriel, and although the Americans have made their way into the Underworld, Asuna and the others will soon be getting some valuable help of their own as Sinon and Suguha make their official Underworld debuts as Goddesses too. There's quite a lot going on when the series makes its big return.
If you wanted to jump back into the series before the War of Underworld arc comes to an end, you can currently find Sword Art Online: Alicization - War of Underworld streaming on Crunchyroll, Funimation, HIDIVE, and Hulu. War of Underworld is described as such, "Kirito, Eugeo, and Alice. Six months have passed since the two disciples and an Integrity Knight brought down the pontifex, Administrator. With the fighting over, Alice has been living in her hometown of Rulid Village. Beside her is Kirito, who has not only lost his arm and soul, but also his dear friend. As Alice devotes herself to looking after Kirito, she too has lost the will to fight she once had as a knight.
'Tell me, Kirito… What should I do?' Nevertheless, the time for the final stress test – one which will engulf the entire Underworld with tragedy – draws relentlessly closer. Meanwhile, in the deepest areas of the Dark Territory, the Dark God Vecta has resurrected, as if to have waited for this very moment. Leading an army of dark forces, they begin their invasion into the human empire in hopes of attaining the Priestess of Light.
The human empire force led by the Integrity Knight Bercouli prepares for a war of an unimaginable scale against the army of the Dark Territory. Even then, Alice is nowhere to be seen, nor the two heroes that saved the realm… The curtain rises on the final chapter of the SAO series' longest and most glorious battle – the Alicization arc."