There is so many time/logic gaps. When did he suddenly picked up some guild quest and teamed up with the Assassin? And it's a bit freaky how rather than being a bit afraid of her or at least troubled and conflicted, he's so impressed.
@Bottersnike@hotel
Probably doesn't help, but the online eng<->jpn dictionary I tend to reference has:
浸透(P); 滲透 【しんとう】 (n,vs) (1) penetration (e.g. market); pervasion (e.g. thought, ideology); (2) permeation; soaking; osmosis; (P)
where (2) leans towards your translation just fine.
捕縄 【ほじょう】 police-man's rope
so with jutsu, it makes it seem a bit more like "how to restrain someone after capturing them" and less "rope bondage" :)
dictionary used http://nihongo.monash.edu/cgi-bin/wwwjdic?1C
even more results if you swap it from the default "jpn-eng general" dictionary to "japanese wordnet", especially for 浸透
@panneqaha thanks! I do actually use a j<->e dictionary (usually jisho.org, sometimes looking for extra clarification on kotobank etc.), I just thought "osmosis blast" sounded a little bit stupid (and "penetration blast" was too horny). Fortunately, this site cleared it up for me with the explanation I translated in the notes.
Also, for some reason I never looked for 捕縄 on its own, which is partly why it confused me
As far as the rope bondage thing, that image was lifted from the Wikipedia article I referenced, so I regret to say, any other interpretation is on you