A lot of the common wisdom you'll find about how to achieve this ranking on the internet isn't accurate, so here's a guide that explains accurately what the deal is with this.

How the 10 Star Rank is calculated:

The 10 star rank is calculated as a score out of 100 points, in order to achieve 10 star you need to acquire all 100 of these points throughout the course of the game. So what are the requirements.

Difficulty:

Easy Mode: -5 Points Normal Mode: 0 Points Hard Mode: 0 Points

Due to later requirements, you are forced to play the game on Hard to acquire the 10 star ranking. But you do not gain any points for the correct difficulty, you merely don't lose them.

Game Clear Number:

5 clears: 10 points 4 clears: 8 points 3 clears: 6 points 2 clears: 4 points 1 clear: 2 points

In order to achieve the 10 star rank, you need to have 5 completed playthroughs already done on the savefile you're trying to get 10 star on.

Ending Type:

Good+ : 10 points Good: 5 points Bad+: 3 points Bad: 1 point UFO: 0 points

The Good+ ending is necessary for 10 star.

Save Count:

0-2 Saves: 5 points 3-5 Saves: 4 points 6-10 Saves: 3 points 11-20 Saves: 2 points 21-30 Saves: 1 point Over 31 Saves: 0 points

Continue Count:

0-1 Continues: 5 points 2-3 Continues: 4 points 4-5 Continues: 3 points 6-7 Continues: 2 points 8-9 Continues: 1 point Over 10 Continues: 0 points

Due to the nature of the IGT, dying and continuing or saving and reloading makes the run not single-segment and thus ineligible for submission anyway, but if you're just playing casually or practicing, you're allowed some saves and continues.

Clear Time:

0-90 minutes: 10 points ~120: 9.5 points ~180 minutes: 5 points ~240 minutes: 3 points ~360 minutes: 2 points ~720 minutes: 1 point Above 721 minutes: 0 points

If you're speedrunning even decently, you'll clear this requirement, but it does mean that 10 star runs intrinsically can't be slower than two hours ever.

Item Count:

Above 150 Items: 10 points Above 135 Items: 9 points Above 120 items: 8 points Above 105 Items: 7 points Above 90 items: 6 points Above 75 items: 5 points Above 60 items: 4 points Above 45 items: 3 points Anything below or at 45 items: 0 points

"Items" refers to literally anything you pick up over the course of the run like bullets and health drinks and such. You need to collect over 150 over the whole run.

Special Item Count:

5-6 Items: 10 points 4 Items: 8 points 3 Items: 6 points 2 Items: 4 points 1 items: 2 points 0 Items: 0 points

Special items refers to the NG+ unlocked by clearing certain endings, so it means the Katana, Hyperblaster, Chainsaw, Gas Can, Rock Drill, Channeling Stone. You start with the Hyperblaster already in your inventory, so it's only necessary to collect 4 other items.

Kill Count:

Ok, this is where it gets incredibly dumb.

Your score for this is calculated according to this formula and what it basically amounts to is that you need a large number of both kinds of kill (shooting and melee), but in a roughly even ratio, if you have too large a quantity of one kill compared to the other even if you have a larger total killcount, you may not acquire the 10 star rank.

Additionally, you may also note the game docks you points for using "Bonus Weapons", this refers to any weapon unlocked via NG+ like the Katana, Hyperblaster, Chainsaw or Rock Drill. But you're allowed more uses of the bonus weapons the more clears you have registered on the savefile, so having a high clear count will enable you to use the bonus weapons more which is genuinely useful in a 10 star run so be aware of it.

You want to get at least 30 points out of this calculation, so plan your route accordingly.

Shooting Style:

This is another bizarre and arcane requirement but the game ranks you according to how many of each kind of kill you got by shooting.

It's calculated according to this formula:

Short Range Shots = A Middle Range Shots = B Long Range Shots = C No Aiming Shots = D

(Ax10+Bx20+Cx30-Dx40) = Your point score, the best you can get out of this is 10 points.

As you can see a "No aiming shot" will decimate your score, and No Aiming Shots are caused by shots that don't hit anything at all or any shot by the Hyper Blaster. The Shotgun consists of a really wide spread of pellets, many of which won't hit the target so using the shotgun at all will push your No Aiming Shots up.

Also, testing has been done on it and it's been found that sometimes shots that totally connected and killed enemies were counted as "No Aiming Shots", so that can also present an issue to scoring the best you can on this category.

At the end of the run, if you've satisfied all these requirements and scored all 100 points, you will achieve the 10 star rank and unlock the Green Hyperblaster.