The following is a translation of the points written on the blog, with a couple of notes by me in brackets:
▪ Right from the start we have Yomako-sensei's story. It's the part that didn't make it into volume 3.
▪ But to have the prologue of the volume where they go to the other side of the galaxy take place on Korehana Island is indeed befitting of the 4th arc.
▪ Yoko becoming a teacher has a lot to do with one thing Kamina said: "I want to let the kids be able to live seeing the sun"
▪ It seems before coming to Korehana Island, Yoko went around to several other schools too.
▪ The scene where Yoko fights off the two criminals has been cut. Surprisingly easily.
▪ Arc-Gurren uses a drill. It didn't use them much in the anime, to the point that they were saying "Arc hates drills" on the radio, so this was good.
▪ Of course, there is also Arc Giga Drill Break.
▪ Father Magin's added story makes me cry for various reasons.
▪ (Believing in Kamina who Rossiu believed in, he got rid of the rule limiting the population to 50 people right after Rossiu left. Because of the hole opened to the surface and sunlight pouring in, even underground, some plants began to grow in Adai Village. After the surface was liberated, he quit being the chief of Adai Village, built a church on his own, and continued to pray. After hearing that they were saved from the moon falling, he came to Adai Village at once and met up with Rossiu there by accident.)
▪ The reason Rossiu tried to commit suicide was to take responsibility in order to wipe away the distrust of the new government.
▪ And yet Simon considers all the things Rossiu did (because Rossiu had the Lord Genome Head and Arc Gurren prepared, they were able to take back the moon battleship; because he evacuated the people to the shelters, the damage caused by the tsunamis and tornados caused by the moon drawing closer was kept to a minimum; because Simon was thrown into prison, he was able to get himself together again and bring Viral in as a comrade) positively, and appreciates Rossiu.
▪ The Dayakkaizer was renamed to Yokokaizer.
▪ The Space Gunmen were already on the Cathedral Terra (Chouginga Dai-Gurren). There are even a lot of spares.
▪ Other than Gimmy and Darry's, the Gulaparls were left in charge of defending the Earth. Gimmy & Darry pilot the "Space Gyanza." (Gyanza was the mech that was originally Gurren. Because the Gulaparls were created in the image of Gurren-Lagann, they are compatible with Gyanza, which equals the body of Gurren-Lagann.)
▪ The reason Viral pilots Gurren is because adult Simon's Spiral Power is so powerful, a person with under-developed stamina can't handle it, but Viral can because he is invulnerable and tough.
▪ Seeing Nia being toyed around with by the Anti-Spiral, not only do Simon and Kittan get angry about it, but Yoko does too.
▪ Zoushi's past.
▪ The middle part of the story has subtly original developments. Apparently he is using scenarios for Lagann-hen that were dropped.
▪ Everyone is safe before they are swallowed by the Death Spiral Field.
▪ This is where the plan to use Simon's Spiral Power as motive power is proposed. But it gives Simon a terrible burden.
▪ Kittan fires a Chouginga Kittan Stinger at the Anti-Spiral when it shows itself, but the Anti-Spiral catches it in its own hand and crushes it, causing him serious injuries.
▪ Space Gyanza cannot sortie in the Death Spiral Field (because while it can synchronize with the Gulaparls thanks to Leite's technical skill, it was not originally made for being used like that).
▪ On top of that, Chouginga Dai-Gurren is attacked by the Nanda fleet, giant dragons that move around in the Death Spiral Field.
▪ The Gunmen pilots (Zoushi, Makken, Kidd, Airac, Jorgun, Balinbow) all end up hitting each other trying to defeat the Nanda fleet.
▪ Kittan also dies by Giga Drill Break. He dies leaving the rest to Simon, Gimmy, and Darry.
▪ Somehow, it seems Kittan knew that Yoko was working as a teacher.
▪ The transformation to Chouginga Gurren-Lagann is accidental. [Not sure if I'm reading that right...]
▪ With the fallen mens' souls in its chest, unmatched in heaven and earth, one machine equal to the gods.
▪ Then the Spirals are attacked by a new mecha, the Vasuki fleet. But despite not having Spiral Power, Viral cuts through them with just guts. "Isn't that right, Kamina!"
▪ This also goes for the sweet dream part, but Viral is oddly cool here. The King of Coordination has been redeemed. [GaoGaiGar reference; Japanese fandom likes to give Viral nicknames in the line of "King of (whatever)" due to being played by Nobuyuki Hiyama]
▪ Apparently Nia used a method of "making her memories into a dummy and affixing them to her own body" to somehow avoid disappearing.
▪ During the final battle, along with seeing Simon pilot the Tengen Toppa, the people of Earth understood that defeating the Anti-Spiral would mean the death of Nia.
▪ After they defeat the Anti-Spirals, Nia spends 5 days going around to apologize to the people who suffered from when she was the Messenger.
▪ The funeral for Kittan and the other Dai-Gurren Brigade Gunmen pilots is a private funeral attended only by the concerned parties.
▪ After Nia dies, Simon leaves the Core Drill in Rossiu's care, and leaves.
▪ 20 years after that, a man with a spiral eye leading a small pigmole digs a hole to make a well in the village of Yakou.
And courtesy of some mild wank on the Nia thread on 2ch, these are apparently Simon's thoughts after he finds out Nia is going to die-
Nia: You've come this far to do what you have to do. Isn't that right?
Simon: (She really is a strong person. I'm proud to have chosen her. I'm proud that she's chosen me.)
....;____; Oh god these two. ♥
And Memusu's name has indeed been changed to Memu in both the novel and the Viral's Sweet Dream story. Oh, and Tsuuma doesn't actually have much screentime Viral's Sweet Dream. Reading some more event reports, I found out the reason why people have said that it's gag-based. Apparently Kamina keeps popping up in Viral's dreams, turning them into nightmares. LOL. XD