The Alcoholic: Issei's not quite there yet, or at least is capable of managing it well enough to abstain when there's a chance it would interfere with his work, but he regularly drinks alone at a bar near the hospital, and comments when the protagonist visits his apartment that "there's nothing here but liquor."
The Atoner: Issei is so haunted by the death of the protagonist's mother that he has no life outside of his work and spends pretty much every waking moment working to provide patients and their families with the best possible care. He keeps a notebook full of the details of every patient he couldn't save, starting with the protagonist's mother. When the protagonist tells him that saving other people's lives doesn't make up for the mistake which killed her mother and the cover-up that followed, he goes on TV to make a public confession about the incident twelve years ago, sends letters to every member of the hospital's board of directors to ensure that his father is removed as director of the hospital, and gives up practicing medicine completely.
Broken Ace: Issei is a brilliant surgeon whose skill earns him quite a bit of recognition in the medical community. Emotionally, however, it quickly becomes clear that he is damaged goods.
Drowning My Sorrows: On Issei's route, the protagonist stops in at a bar near the hospital for a drink or two to try to take the edge off her conflicted emotions. She finds Issei already there, drinking heavily; the bartender confirms while he's not exactly there a lot, he's been a regular, solitary customer for years.
Nepotism: Issei is a genuinely exceptional surgeon who deserves all of the praise he receives for his abilities, but it's clear that being the director's son also allows him a lot more influence at Ebisu General than you'd expect a surgeon his age to have - for instance, dictating the hospital's policy regarding how long patient records are retained. Given how passionately Issei feels about putting patients first, this is generally to the hospital's overall benefit, but there are negative consequences as well: if his father hadn't used his own position as a surgeon to allow Issei to operate in his place, the protagonist's mother would not have died.
Please Kill Me If It Satisfies You: Once he realizes who the protagonist is, Issei is fully prepared to let her kill him, even inviting her to his apartment to give her an opportunity.
Samaritan Syndrome: Issei has a non-super-powered variant. He devotes his entire life to his career as a surgeon and his entire career as a surgeon to giving patients the best care possible, from pulling all-nighters researching new techniques to counseling the grieving relatives when a patient dies. He keeps detailed records of his failures to ensure that he never forgets them, keeping the guilt fresh.
Seppuku: During his Another Story, Issei offers to kill himself if the protagonist tells him to, in order to apologize for the death of her mother.
The Stoic: Doesn't emote much. Irie, towards the end of Issei's route, reflects back on the past several years and describes Issei as never smiling, crying, or even getting angry, as though he were both alive and dead.
Sugar-and-Ice Personality: Issei is outwardly cold and terse, rarely expressing his emotions or saying more than necessary. Underneath that, however, he proves to be a very caring and sensitive person.
Workaholic: The nurses are used to seeing him staying up all night at the hospital to do extra research on the nights when he's not on duty.
Chick Magnet: Junpei is said to be quite popular with the nurses - a statement borne out by Saomi's obvious crush on him - and as shown at a class reunion in his Another Story, at least some of the women he went to high school with would like to have a chance with him as well.
Everyone Can See It: Junpei's feelings for the protagonist are painfully obvious to everyone. Just how obvious becomes abundantly clear in his Another Story - every time the protagonist tries asking for general relationship advice, whoever she's speaking to knows automatically that it's Junpei she's talking about.
I Want My Beloved to Be Happy: He really does just want the protagonist to be happy, even if that means supporting her in pursuing a relationship with Issei, risking his career to steal her mother's records from the hospital, or taking a knife for her.
Leave the Two Lovebirds Alone: In Irie's route of the "Our First Winter" side story, Junpei proves himself the only person in the room with any degree of social sensitivity, herding Kyosuke and Ayame away from Irie's party so that Irie and the protagonist can have some time alone together.
Supreme Chef: As shown in his Another Story, is an excellent cook with a cabinet full of Le Creuset cookware.
Taking the Bullet: Shields the protagonist from being stabbed by the director near the end of his route, taking the knife himself.
Blatant Lies: His excuse for not eating peas. It's not in any way a dislike, he has a "mental allergy."
Cannot Spit It Out: Irie rarely gives away any more information than he can help, a habit which is very useful when it comes to manipulating others for his own advantage, but - as demonstrated in his epilogue and Another Story - becomes much more problematic when he's trying to have a relationship with the protagonist. He ends up causing her a great deal of stress that could easily be avoided if only he'd explain his reasons for doing things instead of leaving her to worry that he's not as interested in her as she is in him.
The Chessmaster: Very skilled indeed at arranging situations and manipulating people to his own ends.
Pull the Thread: Irie is far too perceptive to be fooled by the protagonist, but even when she's obviously lying, he typically doesn't call her on it directly. His preferred modus operandi is to play along and maybe put some bait in her way to see how she'll react - giving her rope and waiting to find out if she's going to hang herself with it or not.
Trade Your Passion for Glory: Along with donning a pair of Jade-Colored Glasses, Irie admits on his route that this has happened to him - he's become so caught up in maneuvering himself into a position of greater power and influence that he's lost sight of his passion for medicine and the reason he wanted influence in the first place, which was to improve options and resources for doctors in rural communities.
The Charmer: Kyosuke Narumi is friendly, sociable, often flirtatious, and generally capable of easily winning over most of the people around him. He's very popular among patients for his ability to put them at ease and make them forget for a little while that they're in the hospital.
My Greatest Failure: His best friend died of cancer a few years prior to the story. Narumi had suspected that his friend was relapsing, but decided not to act on his suspicions when his friend told him he was healthy. He blames himself for not trusting his instinct and not being a good enough doctor to see the signs more clearly and act on them.
Obfuscating Stupidity: Downplayed. Given that he's a doctor, nobody would accuse Kyosuke of being stupid, but he definitely plays the fool and is a lot more savvy and observant than he chooses to appear. It seems to be his way of avoiding getting too tangled up in the messy politics of Ebisu General by ensuring that people don't take him seriously.
Stealth Hi/Bye: Has a talent for appearing out of nowhere with no warning, and for occasionally vanishing the moment the protagonist takes her eyes off him.