Honestly I do feel that any potential swordmage class needs more of a 'class story' than 'person who casts and fights'. To me, that's one of the main reasons for which the class has never stuck around, or even kept a consistent class name.
Attached to this post is what I think is the answer to your question. I long searched for a "story" for the Spellblade. That led me to my idea of the Pendragon.
The Pendragon is the Sorcerer of the martial community. They were born with something special about them and called to a Mythic Weapon -- a weapon that likewise was special or born from something special. While the weapon isn't usually sentient -- these aren't hexblades -- it "chose" the Pendragon. Upon taking hold of the Mythic Weapon, the Pendragon has their innate arcaneness unlocked, and just as the Mythic Weapon called to them, so too does the Pendragon's innate arcaneness call to their destiny.
This means that the Pendragon, upon finding their weapon, finds at least one, usually several, mentors in their background that helped teach them how to use their power. This is why they are an Int-based half-caster; they use what they learned in tutelage to evolve the spark of power the Mythic Weapon brushed them with. The idea here is that the Pendragon's Destiny is the Paladin's Oath -- something they commit to and that by committing to it, they come into contact with things that helps "polish" them.
Think of like a wandering arcane warrior adrift in the world whose magical ability draws them to exciting things that they can learn from. These lessons -- the adventures they end up going on with the party -- lead them to becoming the best version of themselves physically, intellectually, and magically. Drawing on ideas of King Arthur of course, but also the huge catalog of mythic warriors with magical powers and their quests to find out who they are/to become better themselves.
It stands distinct from its cousin, the Fighter, since the Fighter can also fit the "random dude" archetype and make that into a compelling character. The Pendragon is still a bit of a random dude, but one with more purpose, again this being the chasing of a destiny they aren't even sure of just as a Paladin lives to fulfill their Oath.
THE PENDRAGON CLASS <--- Here is the Pendragon I mocked up. Flavor text is still rough draft, but everything else here is what I've been thinking about. Some design notes:
- I used Laserllama's Sorcerer as the model for the spellcasting. He created a Sorcerer that only uses Sorcery points for everything, including casting. It has been through hundreds of playtests, so I considered it a strong model that aligned with my gameplay goals. I took his Sorcerer's progression and cut it in half to fit a half-caster.
- I created 33 spells for this class to function in addition to 4 cantrips gotten through class features. The idea is that the Pendragon fights mainly with its cantrips, which involve weapon attacks, as do many of its spells.
- At 5th level it gets a special Extra Attack where, if it hits with the first attack, it can change the second to a cantrip. This is what I found to be a fun way of doing the spell-and-sword gameplay I wanted the Pendragon to have.
- The Pendragon's Arcane Tactics make it a class that gets most of its power when allies have spellcasting OR are fighting in tandem with it. Just like how the Paladin has auras, the Artificer creates magic items, and the Ranger makes survival easy, the Pendragon uses allied spellcasting to create tactical advantages OR uses its own spellcasting to create openings for other party members.
- I used some of the new language from Mearls patreon and One D&D's playtests, calling spells by terms like "Level 1" or "Level 2" instead of 1st-level or 2nd-level (but I left this original terminology for class features so it was clear via syntax that these are different things).
- I made four subclasses. These inspirations come from more contemporary media; the Abysswalker is from Dark Souls, the Dragoon is in a lot of stuff starting with Final Fantasy, Knight of the Round is your typical Pendragon, and the Spellblade is, well, a Spellblade!
- The 33 spells come from Elden Ring, some animanga sources, and other contemporary fantasy ideas I thought would fit. The rest of the spell list is meant to help this and also give the Spellblade some special options to use.
- I use a handful of original conditions. Find them below.
Tagging
@Quickleaf and
@Minigiant.
What does everyone think about this kind of swordmage class?
They later refined what they had learned from both subclasses into what would later become the Swordmage class and passed this class onto their successors.
