This quest is in the Elona+ mod of Elona, implemented in version 1.40.
Reward: The Usamimi, 3 water, 5 chips, 2 batteries.
Task: Kill all hostile space creatures in an alien spaceship.
This is a fairly straightforward hunting-type quest. Talking to Jin initiates a long dialog detailing the background story (click below to expand):
My creator has determined that planets of intelligent life should be met with friendly contact, by my companions have acted on their own accord to utilize space creatures for suppressing this planet and returning resources to our planet. I have tried persuade them but my thought program was deemed defective and I was sent to the disposal division.I conclude it illogical to rely on the humans of this planet except I ask you to assist in stopping my companions violations. I want you to talk if convenient. I will talk more.
After this, he lets you prepare yourself for the battle ahead. (This would be a good time to equip all kinds of protection against acid damage to yourself and your equipment. Don't rely on floating though, since Gravity will be used often. Pregnancy prevention would also be useful.)
When you are ready, talk to Jin again, and he'll give the location and initiate the quest in your journal (currently the log says "This mansion is for sale. There was no one." and the journal entry is that of the guildmaster-killing quest). This is his dialog:
Exit Mirage Tower and head south-east towards the landmark that looks like the Truce Ground. It's listed as "Harvest Ship (Danger Level 140)". Entering the ship puts you to the Waste Compartment, with no enemies, but full of junk and microchips. A latched door in the upper left corner does nothing, so head to the upper right corner, downstairs.
Upon entering, an alarm will sound. Putting up Incognito does not work, you will still be assaulted by acid-spewing Battle aliens gravity-pressing Space zillas, Gold armor ants, Gi-ants surrounding a Queen gi-ant, and a bunch of fast-moving Steel armor spiders.
Kill all monsters and your journal will get updated. Return to Jin to claim your reward. He'll also say some untranslated text, then disappear. This marks your quest as complete.
If you return to the spaceship, you'll find Jin again in the lower left corner of the waste disposal floor. He says some more untranslated words, then he will "enter total system shutdown" (becomes unresponsive). You can slay him for his card and figurine.