[@Peaceless]I don't believe there are weapons like that in the series to my own knowledge. Though it is a short visual novel so I'll give you that. There so far have only been weapons shown that are standard shooting, or melee weapons. [@Heckno12] I believe has played the visual novel too so he may be able to help jog my memory too. Transformable weapons aren't a thing the closest thing to that would be eagle's ability to shift into overdrive mode which is basically trans-am from gundam oo mixed with G Gundam's Super mode. Though I suppose if you somehow worked in why you'd have an experimental weapon from some company, or your own design then I MAY consider it. Though the effects your stating probably won't be a thing as there is as of yet no standard for 'elemental' effects.

 A shield shouldn't be too out of the ordinary though there aren't none shown in the series I'm sure some mechs have that option. My best bet would probably go with a pistol build and drop the shield as you can spray, and move. Using a sword, or some other melee weapon to keep them from just wiping you out at close. Harass, and delay the enemy prevent them from making moves while my own character, and Heckno's work some sort of play out on the enemy. Or if you wanted a more melee oriented build then using an standard rifle, and perhaps a sword and shield. It's pretty basic as far as mechs go but it works for just general standardized things go. However there are also heavier weapons notable in the game as while some units have slimmer weapons, others have heavier builds like Eagle (The main protagonist's mech) notably uses a large buster sword like weapon.

Does this help at all?