A Spot Of Tea: Englishwoman Leonie is quite fond of it, as is Cabal, who while German born, grew-up in England. They are nonplussed by the Mirkarvia disdain for tea.
Belligerent Sexual Tension: Arguably, Leonie and Cabal. The two of them reluctantly respect and admire each other and when they're not contemplating killing or trying to have the other person arrested, they do make a pretty good team. There's also the fact that the two of them are forced to act as though they are besotted with each other in order to conceal Cabal's true identity, so in the eyes of nearly everyone on the Princess Hortense they are the Official Couple.
Also throw in the fact that Leonie Barrow is the in-universe Expy of the woman Cabal apparently became a necromancer for, and you can see why Cabal's feelings for Leonie are... conflicted.
Berserk Button: Johannes Cabal HATES it when people try to kill him. And considering that he's shot people simply for annoying him, one has to fear the depths of his hatred.
Conscience Makes You Go Back: Much to Cabal's irritation when he realizes that while he may be a criminal mastermind, he still would rather be on the side of humanity than with genuinely evil, opportunistic leeches like Moretti or Marechal which is what prompts him to go back to the aeroship.
Frame-Up: Cabal frames Leonie as a Necromancer in order to distract Senzan authorities while he makes yet another escape. Unfortunately for him Leonie gets out rather quickly and when she finds him again, she is far from happy.
Hidden in Plain Sight: Cabal has a very difficult time figuring out how a murderer or group of murderers managed to kill two people and evade the attention of the airship's crew, until he realizes the captain and crew were behind the killings all along.
Honor Before Reason: Cabal calls Leonie this when she decides to return to the Princess Hortense to finish the investigation because it's the right thing to do, despite Cabal telling her that it will most likely end in her getting killed as well.
MacGyvering: A simple trip to the local drug store and Cabal can create hair dye, reagents to revive the dead, and time bombs.
Noodle Incident: "Cabal could not have been more horrified if she'd pulled off her face to reveal a gaping chasm of eternal night from which glistening tentacles coiled and groped. That had already happened to him once in his life and he wasn't keen to repeat the experience."
Obfuscating Stupidity: Implied with Cacon, who is revealed to actually be a Senzan agent, and attracts Cabal's attention prior to The Reveal with an out-of-character display of intelligence. Also, the seemingly harmless Harlmann turns out to actually be a con artist/professional criminal.
Oblivious to Love: Well, not love so much as lust. Cabal's razor sharp intellect fails him with regards to the wiles of the opposite sex so when Lady Ninuka tries to put the moves on him he is completely lost. Leonie has to spell it out for him before he realizes it.
Spy Versus Spy: Pretty much everyone aboard the Princess Hortense except for Zoruk, De Garre, Leonie and Miss Ambersleigh has an secret identity, mission, or at least an ulterior motive. The first two end up dead as a result of the multiple conspiracies taking place.
Teeth-Clenched Teamwork: Leonie Barrow and Cabal are pretty much forced to do this in order to unravel the conspiracy on the aeroship even while trying to outmaneuver each other.
Testosterone Poisoning: This is presented as being a big part of Mirkarvia patriotism and mores, and is expressed variously in extreme jingoism and a love of unpleasant cuisines they consider "masculine".