The Ascent

Quite an easy achievement. As the achievement description says, you need to get killed by an enemy wielding a katana. You will come across these enemies among the Rojins (see image below), which can be found in multiple locations in the highStreet Tier. During the 3rd main mission, i.e. Trading Places, you will get access to this part of the map.

You can find them either southwest of the Node in the Gemini Stacks, CorpZone and the Umbilical, and north of the Arcology in Tham's Gate and Cosmodrome. When you encounter them, the best way to ensure you unlock this achievement is by defeating all enemies except the ones wielding katanas. After you have done this, all you have to do is wait for them to kill you.

I have also included a short clip to show the katana-wielding enemies and how to unlock the achievement.
Leave a comment if anything is unclear or if I can improve the guide.

Sashimi
You were killed by a katana

This is a very easy achievement to unlock, however if your too good you can miss it. All you need to do is be killed by a Katana, the first time you see these enemies is during the 3rd main quest "Trading Places". There is a mandatory fight as part of the mission that will have 3 of these enemies & only two enemies with guns. Just run away & the guys with swords will case, then kill you. If you have any questions just ask. Here is a video to show exactly what to do.