You control Killia, and add others to your team with the aim of entering dungeons and fighting monsters. By defeating all the monsters in a dungeon, you clear that level and unlock the next one, which get progressively more difficult.
The fighting is turn based, meaning that you place your characters where you want within the dungeon, and decide whether to command them to attack, use an item, or defend themselves. When you're ready, you choose the option to "execute" which sets off the chain of commands you've chosen for each of your characters, and when they're done, you end your turn, the enemies make their move, and play comes back to you. This continues until all enemies or all of your allies are defeated. Kind of like a giant game of chess, only with more fantastical attacks, there's a lot of strategy involved here, as placing your characters in the right place - or even the right formation - can make a huge difference, as characters get bonuses for being positioned near to certain characters, but are also left vulnerable by being grouped together. On the plus side, if you're defeated, your characters don't die, so you can restore them in a hospital area and try again.
In terms of accessibility, with a large emphasis on story, there's a lot of reading involved - however, the text is mainly dialogue between characters, so is also said out loud. The bare minimum of reading required is for the descriptions of items that can be used to help in a fight, for example to restore health or special points (which allow you to use more powerful attacks). That said, Disgaea is a complex game, and you'll need the ability to think two or three goes ahead to get on here, meaning this is one aimed at older children. As a bit of a helping hand, you do have the option to save regularly, and can pause the game whenever you like, so the game can be stopped and picked up again whenever you like.
There are a few sexual references in the game, such as a pole dancing demon, and certain suggestive dialogue, for example a character reminiscing about their past life makes a reference to "lick(ing) a girl's recorder," and the topic of sexual harassment is also present in the game.
There is slight bad language used in Disgaea, with the word "sh*t" being used in dialogue between characters, but this isn't very regular. There is also an item in the game called "Hard Liquor", which you can give as a bribe to someone in the game, causing them to be described as "drunk" or "drunken" when you try and interact with them.