Now this is an challenge.

[magnemoe]

Rescuing an kerbal in retrograde orbit. 

Now I have more than enough dV to intercept. and return to Kerbin, however I will need 18 km/s to enter kerbin orbit. 
An 9 km/s burn after matching speed with the kerbal will take me to an intercept with Kerbin who is prograde so I can just aerobrake in however this will leave me with 4km /s short. 

Not sure if redirecting to Duna or Jool would be any help here. Has Colonies at both, or rater will have at Jool on arrival. 
Think best option is an new ship with more dV. one option is lawnchair final stage 

[Kryxal]

I'd go with Jool, and a MAJOR gravity assist to speed you on your way back to Kerbin.  This can be combined with turning things into a bi-elliptic transfer (apoapsis WAY up, reverse up there for much less delta-v).

[magnemoe]

22 minutes ago, Kryxal said:

I'd go with Jool, and a MAJOR gravity assist to speed you on your way back to Kerbin.  This can be combined with turning things into a bi-elliptic transfer (apoapsis WAY up, reverse up there for much less delta-v).

Excellent point. orbit is around Dress so might be possible to do that turn, has to look into it. 
Life support might well be an issue. 

[Laie]

Yes, something like this even was a proper challenge once. If you're genuinely looking for how other people did it...

On 4/27/2017 at 7:23 PM, Human Person said:

 @Cpt Kerbalkrunch made the 1st entry without using any nuclear- or ion engines. To make this possible, he used Jool-assists to lower his delta-v requirements. The reentry was close to maximum reentry velocities.

He gets the Grumpy Cat prize.

 @ManEatingApe did it the brute-force way. using nuclear- and Ion stages, he was able to keep mission time, launch mass and cost surprisingly low. 

"Rearview mirrow" prize.

 @ManEatingApe made a second, completely different entry to take the cost-record. The mission took literally millennia, good thing Pilots don't get payed per working-hour.

"Who's Jesus?" prize, Longest mission Time (2.3 millennia)

@MarvinKitFox  built an ultra light ion spacecraft to get the job done. The mission took over 36 years and didn't involve any complicated gravity assists.

 

[Aegolius13]

Maybe go with ions,  bring a stupidly large amount of xenon and make the remaining ship very light.   I've used this method for very high dv low solar rescues.  Burns will take forever,  but in solar orbits that doesn't really matter other than your patience.

[Human Person]

Quite a challenge you got yourself there. Feel free to submit your mission to the retro solar rescue- thread. I would be happy to reactivate it.