Well, it depends. The Highschool DxD novel contains some elements such as fan - service, which might not be appropriate for very young readers. It also has some complex themes and battles that might be a bit hard for really young minds to understand.
It's not easy to find it for free legally. Most of the time, the official sources require payment. But sometimes, the publisher may offer some sample chapters for free on their official website.
You can try some popular e - book platforms like Amazon Kindle, where they might have the digital version available for purchase or borrowing if it's in their library.
The Highschool DxD manga has indeed finished. It wrapped up after completing all the planned story arcs and providing a satisfying conclusion for the readers.
If Spawn were to interact with the main characters, he would bring a whole new level of seriousness. He has a dark past and a lot of baggage. When it comes to Issei's goal of becoming a harem king, Spawn might find it absurd but also interesting in a way. He could offer his own perspective on power and how to use it responsibly, which would be a contrast to the more carefree attitude of some of the Highschool DxD characters. And with the other characters like Akeno and Koneko, he'd be sizing them up, trying to figure out if they're threats or allies.