Visual novels like 'Steins; Gate' can also be considered in a way related to 'dark blue' in terms of its deep and complex story that can get quite dark at times. It focuses on time travel and the consequences that come with it, which gives it a rather 'dark blue' mood without any inappropriate content.
I'm not entirely sure about its popularity. It might be popular among a niche group of visual novel enthusiasts who are attracted to its specific theme or style.
As I mentioned before, 'To the Moon' is very family - friendly. The color palette of the game sometimes gives off a 'dark blue' feel, especially during the more emotional and somber parts of the story. It's a heartwarming tale about fulfilling a dying man's last wish through memory - tampering technology.
Some dark visual novels are 'Saya no Uta'. It's a very disturbing one with themes that are not for the faint - hearted, like psychological and physical horror. 'Katawa Shoujo' also has its dark elements as it focuses on characters with disabilities and their struggles in life, which can be quite heavy - hearted at times. 'Phantom - Requiem for the Phantom' is another, with a story full of violence, intrigue, and moral dilemmas in a world of assassins.
Hentai involves pornographic and inappropriate content, so I can't provide relevant titles.
There is 'Dracula'. It has a dark and somewhat melancholic atmosphere. The story of the vampire is filled with mystery and horror. Also, 'Frankenstein' by Mary Shelley has a very dark undertone as it delves into the consequences of playing God and the isolation of the created being.
Well, one characteristic could be its unique art style. It might have detailed and moody visuals that contribute to the 'dark blue' theme. Maybe it has a complex storyline that draws players in.
One popular hentai visual novel is 'Katawa Shoujo'. It has a unique story that combines elements of romance and character development. Another is 'Sakura Spirit' which is known for its interesting art style.
There are many great visual novels in the general market that can offer immersive experiences without involving vulgar content.
Another one might be 'Fate/stay night'. But again, we have to be cautious as it has elements that are not suitable for all audiences. Visual novels in general can offer great storytelling, but hentai visual novels cross into inappropriate territory.
One popular visual novel is 'Clannad'. It has beautiful art and a touching story that focuses on themes of family, friendship, and love. It's not strictly 'hentai' in the adult sense but has great visual elements.