[Snake]

You get no benefits but a drawback, the chance to trigger 'resist' when using Hikage and Tsukikage combo.

I really wouldn't mind Tsukikage's damage to be pathetic, if only it's effects justified it. And this might even be a solution for the whole 'I don't want to use Hikage and Tsukikage' part.

Silence can be taken care of in a blink anyway, so let's limit it a bit. Any sane mage would pack a Throatopener/Screamer Tome/Silent Prayer because they don't want to be locked from their gimmick, so:

Hikage:

'Inflicts Burn LV 25 for 3 Rounds on Critical Hit.'
'If the target is silenced, inflict 'Hellflame Uorate' for 3 rounds on hit.'

Tsukikage:

'Inflicts Silence for 3 Rounds on Critical Hit.'
'If the target is burned, inflict 'Strangling Etacof' for 3 rounds on hit.'

Even though having new effects wouldn't solve this problem, so I'd be down to even their damage, scaling wise, as Spo said. 30% VIT, 60% GUI is pretty much the only reasonable one here, as adding STR would take away the 'Water Element' feel gimmick from it.

Rant:

Assassins are supposed to assassinate a target before they can even react properly, while being really really vulnerable to the people who can survive their burst damage, pretty much Physical Damage Evokers, you can't just take the damage out of them like that. They're obviously going to excel in one-versus-ones, but get ass-kicked in group fights. It's just their playstyle, always been, until the damage part got removed, or just moved to other items, further making stuff 'mandatory'. Even worse when people can do insane damage by using DEF/RES as offensive status. People who build for damage won't get damage, and people who build to be tanky get? This should be really reviewed ASAP. :/