The intro sequence, which is pretty much an Establishing Series Moment for the entire series. Etna decides that since Laharl won't wake up, she's gonna have to resort to shooting him. He wakes up and asks about the weapons behind her, and Etna defends he's a heavy sleeper. When she tells Laharl that his father died two years ago while he was asleep, he grows angry and asks why she didn't wake him earlier, to which Etna responds "what do you think I've been doing all this time?"
The Prinnies try their fins at Laharl's challenge to claim the title of the Overlord. They know they're completely outmatched, so instead...
Enemy Prinnies: We challenge you to a game of baseball, dood!
In Episode 3 of Afternoon's Etna Mode, Flonne confronts Etna at the Sea of Gehenna... wearing a sentai mask. Calling herself 'Justice Flonne', she swears to defeat Etna, and after being chased off the first time, she comes back, claiming to have powered up. All she does is turn on lights where the mask's eyes are.
Etna: That's it? So your eyes are glowing...?
Flonne: Yes. Now, I can see in the dark.
Etna: Anyone who walks around at night, wearing that mask has gotta be some kind of crazy.
In Episode 9, when Jennifer and Thursday meet the Disgaea trio. This is Thursday's response when he senses lifeforms approaching:
Thursday: LIFE FORMS ARE APPROACHING. OH $*&% RUN RUN RUN...!
And in his first scene:
Thursday: GORDON KEEPS STARING AT JENNIFER'S THIGHS. PERVERT - PERVERT - PERVERT!
Vulcanus' reaction to the contents of a book he finds while sneaking around Laharl's castle;
Vulcanus: This page! This page! All of these pages!
Captain Gordon, Defender of Earth!'sglorious introduction.
And his Bad "Bad Acting" when he wants to sneak away from Laharl. "LA LA LAAAA!".
Episode 7's final boss is Aramis' ultimate zombie, which Laharl quickly considers The Dreaded. Is it because it was made with the fists of a Dark Karate master, the legs of the fastest demon in the Netherworld, the mind of the sorcerer Mahogany, and the iron body of Hercules? Nope, it's because it has a Horse Wiener.
Even funnier: if you have a good enough Thief, you can steal the Horse Wiener from the zombie and equip it yourself!
Laharl and Flonne meeting Jennifer, and hearing assumptions that demons are horrible monsters with tentacles, which the two of them take offense to and wonder where she got those ideas from.
After the boss fight with the previous Defender of the Earth, Flonne is angry at Laharl for not throwing the fight and says he's "The worst" before the ghost cuts her off and says that even though he lost, he can still pass on. Everyone prepares to move on, but Laharl and Etna start to wonder what exactly Flonne was going to call Laharl. Thurday promptly states "Now calculating, now calculating," and as he prepares to give the answer, Flonne does a Big "NO!" and slams him into a wall. Etna replies she's worse than a demon. Considering what happens at the end of the game in canon...
Upon catching up with Mid-Boss, Gordon, Jennifer, and Thursday do a hammy Power Rangers-esque pose. Flonne gets jealous that they're stealing the show and forces Laharl and Etna to go along, and their presentation is so damn unenthusiastic.
Etna: Get your mind out of the gutter, Prince. This ain't no hentai game.
Kurtis makes his return to help the party when they're blocked by powerful demons in Celestia. It's supposed to be a triumphant moment, but it's hard for the characters and the players to take it seriously because he's a green Prinny.
In "War of the Netherworld, part 2", as the party boards the battleship Gargantua, Gordon surmises that Carter might have ordered for Jennifer's modification. Laharl, Etna, and Flonne then begin to imagine what the modified Jennifer would look like and we're treated to an image of a Humongous Mecha Jennifer with drills for breasts. Gordon twice has to get them to wave away the image.
Later, we finally get to see the modified Jennifer, and she looks no different from regular Jennifer. Laharl, Etna, and especially Flonne are disappointed.
One of the goodies that comes with the limited edition of Disgaea 1 Complete is a "Noppai" mousepad of Etna. In other words, it's an oppai mousepadnote a type of mousepad that has a portrait of a character with a wrist rest in the shape of the character's breasts...that's completely flat, reflecting Etna's flatness.