To obtain obtain and play with last weapon, cause in Story mode when you finish last map and obtain this weapon, game ended at that moment and you can't test that weapon even. Deleted the game then Story mode was finished though.
You mean the Bombard Alpha and Bombard Beta weapons that you can get in the last two maps on the Ice Field? You can absolutely get them both and use them before ending the game. It's all a matter of how you handle things... and I honestly expect most players that are new to the genre, but stick to it, to end up doing what I did.
Basically, you don't HAVE to rescue all three girls ASAP. Primarily, you need to rescue Hilde from the Hills to unlock the Armory and Frederica from the Desert to unlock the Cell Gear upgrades... but there's nothing stopping you from doing 30 minute deploys in the Hills and Desert after that to unlock the weapons and passives in all six areas. This will leave those areas with an exploration rating of 80%. You don't need to do this for all areas before rescuing Eldfriede, just one.
Now, the trick is that once you rescue her, you'll get the Hyperdrive fix mission... but you don't have to do it in any specific order... which lets you leave any previously cleaned areas for last... like say, an Easy Hills mission, or anything at all really.
You can do the areas in any order, max out the girls, and leave that one area for last and collect the Hyperdrive from it whenever it's convenient for you.
As a side note, the Bombard Alpha and Beta weapons combine with the Speed passive to form their Superweapon, which frees up a weapon slot and opens it up for another basic weapon. The Superweapon in question also has 8 or 9 levels, I don't remember exactly, which makes builds aiming for it the ones that need the highest possible levels. Neither the basic weapons nor the advanced version felt all that great though... They're turret types, but I didn't test to see if they benefited from Frederica's talent, and their attack pattern and area of effect is... weird.
They fire projectiles that explode in a specific area, at the destination, and the projectiles do damage ONLY when they explode, not during travel. Combined with a complete inability to aim the thing, whether it hits anything or not will depend a lot on luck outside of big clumps of enemies in ideal range... and even then you can't guarantee that the stupid thing won't fire on the one enemy that's in perfect range at the time, rather than the clump of enemies that will be in explosion range.
So yeah... not a fan... especially since the Speed passive is the most useless of the lot for anyone other than Elfriede, and Elfriede doesn't benefit from this weapon in any way as far as I can tell.
This leaves the Rocket Funnel as the only weapon that can't evolve in any way... unless there's a secret evolution for it that isn't tracked in the Armory. I doubt it... but it'd be neat if that was the case.