Jin's strings are horrible, sorry. 5d/6c > dash are TERRIBLE; anyone with any Jin experience will rape you for it. 5d/6c > 236B/C against certain chars (noel/ragna/dp chars) will also get you raped.
Umm...I really have no advice; just wanted to say Jin is garbage lol; 6d is OK in strings(after 2aaaa, etc), and crossup j.d is pretty GDLK. otherwise, if they are american and they block the beginning of your string; it's better to stay out of their counter range and just throw a shitty fireball.