When I first started reading novels, I came across this idea. My perspective might be unremarkable, but I've seen it in numerous anime and manga where the main character gets knocked around by foes, friends, and even romantic interests, yet they recover and carry on as if nothing happened. This might have influenced my thoughts, but ultimately...
The book was enjoyable for me, even though the writing style wasn't a major concern. It made sense within its context, with the translated parts being solid, while the machine translation could have been better, but it didn't detract much from the story.
The dark beginning initially caught my attention and helped shape the character's growth, making him mature sooner than expected. Some reviews, especially the negative ones, criticize the main character for being an unlikable jerk with a harem, and some girls getting hurt along the way. But remember, this is a harem story; it's inevitable that he'll attract multiple female characters.
People seem to struggle with the concept, but consider the circumstances: he's been through a lot of trauma, forced to survive in a grim environment with those who betrayed him as his last connection. If not for the loli vampire, he'd likely be a brooding demon lord.
He's a complex character, a Tsundere. People often have difficulty accepting this dynamic when it happens with male characters. He's human, grappling with his emotions and the pain of betrayal. He doesn't kill everyone out of anger; instead, the girls become a source of warmth and help soften his cold exterior. As he struggles to overcome his past and cope with his emotions, his protective nature intensifies, often manifesting in half-hearted explanations to save the day.