It's not confirmed just what kind of love Leaks felt for Shui. Are his feelings romantic, or only platonic but nevertheless deep?
Some have wondered if Shui is polyamoric. He clearly loves his wife, and while he has explicitly stated that he loves Leaks as a friend, his interactions with Leaks make their relationship teeter on the line of ambiguity.
Broken Base: While not a very heated topic, there's still some who question whose is the "true love interest" of the story: Rai and Bardo (while Asato is well-loved by the fans, his route leaves a lot of questions unanswered, and Rai and Bardo's routes have a much more complete plot resolution). Some argue that Rai's route is longer in terms of content, with his relationship with Konoe being more explored and advertised, and Rai himself has the largest fanbase among the three; the other half argues that Bardo's route has a much more concise storyline, everyone's issues are resolved by the end, and it's not like his relationship with Konoe lacks any substantial development. On the other hand, Rai's route is the easiest to get and functions as a default of sorts, which is rarely the case for a "true route" (compare with Togainu no Chi, DRAMAtical Murder and Slow Damage, where the true route is the last to unlock). That aside, the complete epilogue with the full story of Leaks and Shui plays after getting all three good endings, no matter the order. So it's more likely that no "true ending" was intended in the first place.
Tokino is essentially only a side character, yet is adored by many fans.
While all four of the devils are well-liked by the fandom, Kaltz is easily the most popular for being the Token Good Teammate, for his design and personality, and for being Asato's long-lost father.
Kagari is loved by fans due to being an Action Girl who doesn't exist to get in the way of a romantic relationship, and one of the very few characters who cares for Asato.
Despite being the villain of the game, Leaks is nevertheless loved by the fandom for both his character design and his backstory. He's even widely agreed to be the best villain in the Nitro+CHiRAL franchise. While Slow Damage (which came 15 years after Lamento's release) eventually introduced Maya, who is touted by many to be Nitro+CHiRAL's most terrifying and effective villain, Leaks is well-liked even by then and he himself is still regarded as the most sympathetic villain who is also complex and has plenty of development and a tragic backstory.
Shui is widely popular, particularly due to his relationship with Leaks, and being Konoe's father. Not to mention, his kind, gentle, friendly and Adorkable personality immediately warmed himself up to everyone who played the game.
Bojyo (the shaman) is also somewhat of a fan favorite due to the sheer mystery surrounding his entire character.
Fan-Preferred Couple: There's a very sensitive war going on until today about who is Konoe's best choice as his partner. Considering he has three options it's not an easy discussion, but Rai seems to be the favorite of the majority.
Hilarious in Hindsight: While understandable, the words "osu" and "mesu" (which refer to a male and female animal, respectively) are mentioned a lot in the game. Then comes sweet pool, where both words take a whole new meaning...
Froud and Verg count to an extent. While they currently no longer have any sense of morality at present and indulge in their most basest desires, even if it means resorting to underhanded or outright evil tactics to get what they want, there was once a time where they were normal human beings who only turned into devils in the first place from all the abuse they suffered in their mortal lives.
Moral Event Horizon: While Leaks is a pretty despicable guy in general, using Firi's life to power himself up is what makes Konoe decide to never forgive him.
Tough Act to Follow: sweet pool and DRAMAtical Murder are by no means subpar visual novels, with the latter being extremely successful that it spawned a sequel, an animated adaptation (plus an OVA), a Polished Port, several drama CDs, short stories, a wide array of soundtracks, and various merchandises. However, there are some fans who believe that the following games that Nitro+CHiRAL created or will create after Lamento will always be somewhat inferior in terms of overall quality, especially when it comes to the writing.
The Woobie: With the exception of Tokino and a few other minor characters, there's not a single character who doesn't belong in this category.
. It even has a list now.