I want to ride my bicycle
Invoke - bonuses to bike riding
Compel - you feel compelled to ride your bike at all times and feel naked without it.

Another one bites the dust.
Invoke - You're good at killing people...
Compel - ... but you're an awful cook!

I see a little sillowetto of a man.
Invoke - You're good at spotting sneaky dwarves.
Compel - You're not very good at spelling

Indeed, unfortunately you can only do what type of action at a time with evocation, that's the power of ritual magic. The only exception is a grapple, being both an offensive block and a grapple.

Hmm... perhaps if you created a 'defensive grapple' using the same rules. An orbius style spell but rather than blocking an enemy for the duration, dealing one damage each exchange, you put the block on yourself and you deal one damage to anyone that tries to beat the block. It's not much but it's something. In fact, if this is workable (and I'm just throwing ideas around here, this certainly isn't in the book) then rather than deal 1 shift of damage to attackers, perhaps you could push them one zone away e.g. some kind of telekinetic barrier or air barrier; just like the grapple rules state (YS211).

Other than that, yeah the rules only allow one type of action at a time.

One thing about the comic book and Anime version the Witchblade takes over the host because it is a symbiote and burns out the wearer usually killing them as well as trying to take them over.

Add in Demonic Co-pilot? As you use it, it deals you mental stress which will eventually cause consequences, potentially leading to extreme consequences which changes aspects in line with the Witchblade's agenda until eventually you're a tool for the Witchblade, instead of the other way around.

Yeah totally, I hadn't thought about human form. Though psychometry could be used in human form I imagine, that would be at the GM's discretion though.

Do you think it'd be possible to tag the aspect to make the declaration 'the weapon has increased it's weapon value by 1 while the aspect is in effect'. Do you think a GM would agree to that?

Thinking about the numbers it's pretty fair. Instead of tagging for a +2 to hit, you're getting 1 additional damage each turn you use the sword. Of course the next turn you could pay a fate point for +2 to hit as well as the extra damage, but then it's not that different to paying a fate point to invoke a different aspect and getting +2 total, or +2 to in consecutive exchanges.

If this is possible, do you think it's possible to cast a 6 or 7 shift manoeuvre to declare that the weapons value increases to +2?

Yeah a resources declaration might well work as well.

Ah well, since I'm not conjuring a literal sword so much as a physical shape to contain fire wouldn't that change things a bit? This is, again, kinda the crux of the thing. The whole "sword" meme is really throwing off the perception of the result. It's a fuego spell in a tube you can hit people with. So the damage would be dependant on the power you put into it on creation I would think.

Indeed, my suggestion below assumes an ectoplasmic handle with a blade of fire. Ritual is capable of producing fire and ectoplasm so I see no reason why this couldn't work.

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Whether the OP is using an enchanted item for this, or whether it's a ritual he casts to create the weapon, both requires a high Lore and so we'll assume a Lore of 5.

1) A ritual. 2 shifts for complexity and 3 for power to create a Weapon:3 sword. It can be an elemental blade, like fire or spirit, or ectoplasm if you like, so it can satisfy a fire catch but it couldn't satisfy a silver or cold iron catch. It's default duration is one scene or 15 minutes, whichever is shorter. You can add additional shifts for more damage (increasing the heat of the blade or whatever) or duration, or to add an aspect like 'burning blade', but then the ritual will take additional preparation, right now it is only 5 shifts of complexity so you could do it in 5 minutes. This would be more useful if you had sponsored magic.
Benefits - it is easy to replace, doesn't take up item slots, it's form can change to satisfy catches. Can be used for defence against weapon and fist attacks.
Drawbacks - takes time to create, it's a relatively low weapon value without lots of shifts

2) An Enchanted item.
An innocuous looking silver rod, about the size of a mobile phone and wrought with cunning runes, when activated a beam of fire leaps out of one/both end/s
Let's assume two enchanted item slots as you can't do much with half a focus item.
A Weapon:5 attack, three times a session.
A Weapon:4 attack, five times per session
A Weapon:6 attack, once a session.
You choose what kind of damage it will do at creation i.e. it's a fire blade. The actual item might just be the hilt and so it's a small object, easily hidden. Once you're out of free uses you can still activate it, but it requires one mental stress each time.
Benefits - can be used without preparation, it's easier to contruct. With a lore of 5 you can get it up to weapon:10 with additional slots, does more damage, might look like a sword but isn't one and so can be used at a distance (think force throw with it flying back to you, or just launching the blade only), can use discipline to hit
Drawbacks - takes up slots, form can't change, can't be used for defense*

*stick another slot in for a block and you can, like so:
2 enchanted slots -
  Weapon:4 attack, three times per session
  Defensive Block:5, once per session.
Again, you can take inspiration from the jedi as the blade leaps to defend you from bullets, spells and in close combat.