I see, but that's just how koreans talk. Uncle called Jungwoo's mom "큰 누나 keun-noona" which means older sister (with a bigger age gap than just noona), but it doesn't mean they are related - just that they know/knew each other. "친누나 shin-noona" is the only way to specify sister as being related by blood/family. While living in Korea my younger friends call me unnie and noona, and I call my older friends unnie too.
It may be a very stupid question, but I don't freaking understand WHO or WHAT EXPLODED??!!??!
There was a bomb in the factory and instead of escaping with Kot-nim and letting the factory blow up, they left the girl with their friends on another ship and brought the bomb with them into space. So the bomb exploded without hurting anyone, except for the bad guy. Kot-nim protected them by using the nanobots that she can control, otherwise the crew would've died to save the earth and everyone.
I didn't understand what happened to Sun-i in the end...
He got to talk with her one last time through the nanobot connection, before she drifted off and it was too late to save her (they mentioned earlier that the 3 year period where they could save her was almost up, that's why he was so desperate to get the money to find her in time).
Part 1
https://www.youtube.com/watch?v=PsGI1LJn-7Q
Part 2
https://www.youtube.com/watch?v=estp_6mHi1s
This one has Eng Sub if you click the top corner of the video and choose subtitles
This one has Eng Sub if you click the top corner of the video and choose subtitles
https://www.youtube.com/watch?v=btqgzNnqub0
Part 2 is linked on the side