"Mental Ruvajin's" ink-blast wasn't the gutsiest of maneuvers, but one Ryuuga expected. He
is a squid in this realm, after all. The tentacle and beak attacks are a bit distracting, but don't seem to have done any damage...yet. Still, he needs to focus if he's going to get out of this trap. As such, he begins honing his mental senses, just as Ruvajin instructed.
Ryuuga thinks back to his teachings from Kouga-sensei...
Spoiler (click to show/hide):
"Zanbo Mugenjin utilizes two forms of internal energy: Chi, and Ki. Chi is power drawn from the body, and is used in the form of offensive strikes, grounding your feet for defense, and various other physical aspects. Ki is power drawn from the mind, and while it has far fewer limitations than Chi, it is also much harder to actively make use of. In regulating your Chi flow, you use a certain degree of Ki to direct that flow, and focus it on the point of release. There are other ways to utilize Ki, but those who can do so are few in number. Some call them 'Psychics,' or 'Adepts,' but the fundamental trait is still the same: they draw great power from within their mind, and release it in extraordinary ways."
"Ki is power drawn from the mind"...then Ki must be his equivalent to Chi in this mental form of combat. Like Kouga-sensei said, however, it's difficult to wield, yet has few limitations, so he'll need to concentrate on flowing that Ki in ways to help him reduce the hindrance of the ink. It currently has the greatest effect on his sight and smell, so he focuses instead on his sense of sound. He must listen in for the faint slithery sound of an inbound tentacle, or the breath from the squid's beaked maw. With those cues, he can zero in on the target's location.
Once he gets a clear idea of where Ruvajin's squid form is, Ryuuga darts towards it, but off to his right (i.e., the squid's left) side, still focused on quick movements for evasion, and prioritizing the senses of hearing and touch over simple sight, at least until he's clear of the ink. He cuts through any inbound tentacles along the way, then moves up on the squid's left flank, ready to cut it open (unless Ruvajin tells him to stop, for his own safety; still not entirely sure what'll happen if Ryuuga actually kills the squid).