The only valid reason to watch this anime would be to increase your number of 'watched' anime.
Assassin's pride is terribly directed and makes a complete mess of what could have essentially been an interesting story. It is rushed and the plot is thrown around aimlessly. To give you an idea of how rushed it is, the anime adapted more than 500 pages of the manga in just the first 2 episodes.
The anime chooses to gloss over everything and just throws the important points in your face like a TL;DR note, with the exception of somewhat decently depicted fight scenes.

The characters are bland and lifeless and the various flashbacks from their pasts feel pointless by the time you've watched 6 episodes. You feel no investment in any of their relationships with each other nor do you feel any emotions as they go through their ups and downs.

The world building consists of only a 3 minutes montage at the start of episode 1 and then the anime decides to not provide any more information about the laws governing it, how mana works and so on, assuming that the viewer is smart enough to just magically understand it all.

Coming to the extremely incoherent plot, the story revolves around an extremely skilled assassin, Kufa Vampir, who is hired under the pretense of tutoring a young girl, Melida Angel. Melida belongs to a class of nobles who boast a proud lineage of the best class of fighters a.k.a. Paladins. However, Melida shows no signs of having any mana affinity and hence is assumed to be an illegitimate child born out of her mother's affair. Thus, Kufa's true mission is to find out if Melida has any potential for mana and if she doesn't, he must assassinate her to prevent her from staining the Angel household's name.
Obviously she doesn't have mana abilities but Kufa develops a soft spot for her and forcibly awakens her mana using his own, thus turning her into a Samurai class like himself, instead of a Paladin, as was expected from an Angel. Now his sole purpose is to make her as strong as possible so that nobody will try to oppose her or attempt to uncover the truth which will eventually lead to the discovery of Kufa's betrayal to his employer.
The rest of the story is all about different events with shallow characters and every single episode feels pointless.
The 13 year old Melida has a massive crush on Kufa and doesn't attempt to hide it resulting in a very awkward half-hearted attempt at slapping a romance genre tag to this terrible excuse for an anime.
Kufa is completely devoted to Melida, seeing as how her growth is directly related to whether or not he gets to live, and thus calls her His Pride or His Little Lady.

The animation is probably the only good aspect of this anime, as is the OP and ED.
The soundtrack is fairly decent and so is the voice acting.
Other than that, this anime is a pain to watch.
I found myself watching some parts of it at 4x speed, just wishing it would get over.

Trust me and save 4.5 hours of your life by not watching this trash.