No More Heroes: Heroes' Paradise

Naomi’s lab unlocks after ranking 9th and is displayed as a blue-white sword icon on the map. After buying a katana you will have to exit and re-enter the lab in order for the respective parts to be available for purchase. There are three kind of upgrades:

•    Accelerator – A sensor that can locate buried treasure when attached to the handle of the beam katana. (You only have to buy this upgrade once)
•    Power up – Makes your attacks more powerfull
•    Energy Saving – Increases energy efficiency. (in Tsubaki MK-III’s case, you will have an infinite amount of energy and you will never have to recharge your katana.)

The katana’s and their respective parts:
Blood berry – You start off with this and it has no upgrades.

Tsubaki – LB$ 98,000 (available after ranking 9th in the UAA)

• Power Up I – LB$ 29,800
• Energy Saving I – LB$ 29,800
• Accelerator – LBS$ 29,800 (available after ranking 9th in the UAA)

Tsubaki MK-II (Available after ranking 6th in the UAA)*

• Power Up II – LB$ 29,800
• Energy Saving II – LB$ 49,800

Tsubaki MK-III (Available after ranking 3rd in the UAA)*

• Power Up III – LB$ 99,800
• Energy Saving III – LB$ 999,999

* Some people have reported not being able to buy the katanas during the abovementioned ranks. mccrash has found a solution for this:

I can confirm that you can obtain Mark II and III the same time you bring the new parts to Naomi. Just bring them to her, then do anyting else for at least 15-20 minutes except travel randomly through the city or go back and forth from Naomi's Lab. The key is to let the game "reload" the main map a variable number of times (for example, by doing some jobs or missions), as like it does anytime you rank up. By doing this for 20 min or less, you can go back to Naomi's Lab and buy your brand new sword.

Having all of the katana’s will allow you to view the real ending after ranking 1st, the parts however are not required for this matter.