On a similar note, Phoenix and Gumshoe are all varying degrees of nice and personable. But if you committed murder they WILL find you guilty. When Maya's life was at stake Gumshoe became competent. GUMSHOE.
In Aya's epilogue for Akatsuki No Goei, her father finally finds out about her relationship with Kaito and tries to fire him. She instantly grabs his arm and shows that Boobs of Steel is actually quite consistent by nearly breaking his arm before he agrees to hold off on a decision temporarily. Further, the robot Yuuki is the most easygoing of the bodyguard class, but he's still a robot. Even Tominori quickly caves in when he makes Yuuki mad. Notably, Yuuki is the one person Kaito quite possibly could not beat in a fight.
Hatoful Boyfriend: The gentle narcoleptic teacher Nanaki Kazuaki turns out to be Cute But Psycho in the "Bad Boys Love" route, as well as an identity thief who betrayed and murdered the original Kazuaki, as part of his plot to get revenge for his dead childhood friend Nageki. During BBL, he pulls a gun on the characters, then tries to murder Ryouta for his liver. Possibly an inversion, since it seems the "kindly teacher" persona is a facade.
In the sequel Holiday Star we learn that the original Kazuaki is not immune... not since he became The King.
Yuuya is no slouch in the original game, either. Initially seen as a friendly, harmless, Chivalrous Pervert, he reveals in "Bad Boys Love" that he's perfectly willing to kill, he dismembered the human girl, and in the backstory, he crushed an egg belonging to his stepfather, which is basically infanticide.
Zachary is one of the friendliest characters in The Letter, but if he enters a relationship with Hannah, he won't hesitate to punch her husband Luke when Luke threatens the group with a knife in desperation.
Beware all the nice ones in Nine Hours, Nine Persons, Nine Doors. In particular, hurt either of the affable and helpfully sharp Brother–Sister Team of Snake and Clover and the other will rip you to a ragged pile of shreds on the spot; bumbling Big Guy Seven is a former highly successful Cowboy Cop detective and rescued the players of the first Nonary Game singlehandedly; soft-spoken, peaceful, cute-as-a-button Love Interest June is in fact Zero and the game's chessmaster; and even jokester everyman protagonist Junpei is quite an expert Guile Hero when he needs to be.
Taken to logical, if slightly terrifying extremes in the third game in the series Zero Time Dilemma. Akane, though still much smarter than she lets on, is no longer quite the all-knowing chessmaster of the first game. Having used Mental Time Travel to go back several decades, enacting the final part of her grand scheme to save the world means her no longer knowing everything that will happen in the game's timeline, causing her to be far more on edge than usual. As well as this, in the years spanning between the first and second game she realised that her life trying to obtain the greater good was quite miserable and lonely, and promises that after going back in time she will keep Childhood Sweetheart Junpei alive and happy. Despite keeping up a cute, Yamato Nadeshiko-esque act during the Decision Game, if Akane catches Carlos in the act of killing her now Living Emotional Crutch Junpei, or suspects him of doing so, she will either beat him to a horrifically ironic death with a fire extinguisher or turn off all the electricity in the bunker and attack him with a chainsaw. Beware the nice ones indeed.
Accel in SC2VN is the nicest and most caring player that you meet. But when his coach blames him for his team's loss, he willfully abandons his team mid-contract, knowing full well how much drama this will cause.
Yo-Jin-Bo could arguably apply this trope to all the guys except Ittosai. However, special mention must be given to both Bo, the highly chivalrousBishounen fond of kissing your hand, and Mon-Mon, the goofy monk. Bo cuts Nobumasa in half vertically and Mon-Mon punches through his chest and crushes his spine. Ouch.
When Aeka told Antoinette to kill her in Yume Miru Kusuri to just get it over with and kill her already instead of needling her, it wasn't her being suicidal. It was a warning that if you keep pushing her she's eventually simply going to snap. The route ends with Kouhei taking down the gang trying to rape Aeka single handed before he starts strangling Antoinette. Aeka tells him to stop... so that she can do it. They throttle her together until she shits herself at the verge of death, both unwilling to take more abuse from her and wanting to end it here.