Celibate Hero: How he starts. He doesn't stay like that, obviously.
Bi the Way: While he says he's uninterested in sex and wants to focus on anything but that, Masataka soon starts feeling attracted to both Sakurako and Souma, much to his own shock and embarrassment. Then things start going From Bad to Worse...
Child by Rape: The reason why Masataka's birth mother hates him. She then pretty much "sold" him to the Tagamis when he was six.
Happily Adopted: Sorta. The Tagamis paid much more attention to Mitsugu due to his weak health, but they didn't exactly abandon Masataka either.
The Unfavorite: He feels resentment over his younger brother Mitsugu so he often tends to act cold to him, while Mitsugu obliviously clings to him to try have his attention.
Cooldown Hug: To Masataka, after the torture and rape deal with Katsuragi. Somewhat subverted since at first Masataka rejects him, and it's only after Souma promises to not go beyond and keeps his word that Masataka lets him do it.
And again, he gives another to Masataka when he explains his backstory and issues almost at the end, which concludes with poor Masataka having an Heroic BSOD.
Driven to Suicide: As a kid, he thought of giving himself as Slashed Throat due to his deals with Katsuragi but couldn't bring himself to do so. Later he tries to go the Bath Suicide way after realizing how badly he had broken Masataka.
Loving a Shadow: Has completely idealized his long-lost love, Souma's dead mother Abigail. To the point of periodically asking Souma, who's a dead-ringer for her, to put on her shawl and let his hair down so he can sort-of speak to her.
Reasonable Authority Figure: Subverted: while he's not a bad and horrible person, not only his health has taken a nosedive, but he's unable to handle the family business and thus Souma is the one who does so.
Madwoman in the Attic: After an incident during a Cherry Blossoms pasrt, Youya/Sakurako was locked away in the old house, with Katou as their only caretaker and constant company, while everyone outside the manse thought s/he had died of illness. S/he only got out when a fire broke in and Terashima died.
The Unfavorite: Became this when Souma was aknowledged and taken in by Lord Saiki. This is what drove the original Sakurako to madness and to all the Souma abuse, as revenge for her child being shoved aside in the succesion.
Walking Spoiler: Sorta. She appears rather early in the story, but a good part of her motivations are driven by a massive secret in the past.
Jerk with a Heart of Gold: Harsh and rough around the edges, but basically a kind and hardworking young man who loves his baby brother. He's also the only member of Masataka's birth family that he's more or less in contact with.
Ill Boy: Has been thrice in the brink of death. And one of them happens when Masataka is in Tokyo, so the Tagamis send him a telegram and ask him to come back home for a while.
Innocently Insensitive: Subverted. Mitsugu clung to Masataka which caused him to reject him, but later he revealed that he was very aware of the tensions between them and even confesses that he almost wanted to die because of it. Masataka calls him foolish, but from then on they start getting along better.
Abusive Parents: Off-handedly mentions that his mother abused him. He also has a flashback of his teenage self tied up to a cherry tree, but not many details are given.
Bitch in Sheep's Clothing: He appears at first to be a handsome but stoic doctor. Then we're led to believe he's a shady but not really evil guy, even getting an apparent Pet the Dog moment via supporting Masataka in public. And then we get to see what an horrible person he actually is.
Humiliation Conga: The three persons he abused the most become the key to his perdition.
Master Poisoner: Katsuragi made his own drugs and poison, using hemlock and arsenic among other things. Considering that he poisoned Lady Saiki to death and later slowly started to do the same to Lord Saiki...
Rags to Riches: The backstory shows him as as a low-to-mid class highschool student who lived and worked in the Saiki's Big Fancy House. When we meet him, he's one of the top doctors in a local hospital and the personal physician of the Saiki clan.
Letting Her Hair Down - Slipknot Ponytail: When Souma has sex with her to get info about what Katsuragi did to Masataka, Asayo's long black hair (until then arranged in the traditional Japanese manner) goes loose.
The Ophelia: By the time we see this poor girl, her eyes look dull and her expression is vacant. She then attempts to get info about Souma's well-being after his suicide attempt and asks Masataka if he has stepped into the warehouse, but as she's speaking to him she briefly sees Sakurako around and starts screaming... The next time we see her she is smiling madly and tells Kitamura that she believes Sakurako tried to kill Souma, just like she did to her and Souma's baby. Poor, poor little girl.