After you view the Happy End for the Grand Route, in the "Treasure Box" (玉手箱) section, you can select this action game.

You control Kei, the main character from "Akaiito" and go around defeating groups of oni.
I think it brings to mind one of the endings Akaiito, "Onikri no Oni.

There are 3 stages in all. The first stage is the same stage you play when you make an "emergency exit" (Pressing the Home Button during the actual game).

There is music and CG that only appear in this mini-game, so for those interested, please take up the challenge.

Basic Controls

Items

Let's go through tactics on how to deal with the boss of each stage.
At most, this is how I played through this so there might be more effective ways than this.
Also, I haven't put emphasis on a high score. Apologies for that.

In addition, one common pattern to use against all the bosses is to use the special attack when the boss in in the corner.
Since it's quite strong and does multiple hits, it will shave off quite a bit of stamina.
If you continue to activate special attack until your gauge is used up, you can cause a large amount of damage.

An enemy resembling a vampire who appeared in the manga version of Akaiito.
At the beginning, she repeatedly uses Pattern 1 and Pattern 2.
When her stamina gets low, then she'll use Pattern 3 and also Pattern 4.

Attack Pattern 1
Repeatedly using slicing attacks along the ground along with teleportation.
After the slicing attack and before she teleports, there's a little bit of an opening so it would be good to attack during that time.

Attack Pattern 2
Floats in the air while summoning ordinary enemies.
During this time, you can attack Bat Girl using a jump attack (or depending on the situation, a double jump).
If you leave the small-fry opponents alone, they'll fill up the screen, but there's really no need to defeat them.
For those people used to it, it shouldn't be too difficult to jump and dodge the opponents on the ground while attacking Bat Girl in the air.

Attack Pattern 3
Four copies of Bat Girl appear on the ground and attack one by one.
Three of them are fake. If you attack a fake one, you won't deal any damage.
After the four of them appear, the first one to attack (she's slightly brighter than the other three) will be the real one and you can attack her.
You can jump to dodge her slash attack.

Attack Pattern 4
In mid-air, transforms into a crowd of bats and slowly drifts down, after which she dash back and forth along the ground to attack.
Since attacks won't harm her when she's in bat form, there's nothing you can but double jump to avoid the dashing attack and wait for her to return to another attack pattern.

A large red oni who holds a long sword
According to the fan book, it seems to have been an enemy in the Drama CD.
At first, uses Attack Pattern 1.
After receiving some damage, uses a mixture of Attack Patterns 2 and 3.
At the very end, he uses Patterns 4 and 5.
If you continually use your special attack when the large oni is in the corner, it will be easy to defeat him.

Attack Pattern 1
Attacks by swinging his large sword down.
Be careful since the reach is longer than it seems.
In addition, when the sword strikes the ground, there will be a earthquake for an instant.
If you're on the ground at that time, you'll take damage.
You can safely avoid that by double jumping.
After he swings his sword down, he'll leave himself open so you should counterattack at that time.
However, if you're too greedy in attacking, you won't be able to avoid the next attack so be careful.

Attack Pattern 2
Makes a light jump that doesn't suit its large body.
When it reaches the ground, an earthquake will occur.
If you're on the ground at that time, you'll take damage.
The length of the earthquake is unexpectedly long so you should double jump to safely void it.
After you come down from the jump, counterattack.

Attack Pattern 3
He thrusts his sword into the ground, causing a shockwave to appear on both sides of him (sort of like a Power Wave).
Since there's no earthquake and the shockwave's reach is short, it's no big deal.

Attack Pattern 4
He thrusts his sword into the ground, summoning two normal enemies (dead spirits).
As long as you do not defeat the spirits, they'll keep chasing Kei, which is annoying.

Attack Pattern 5
He thrusts his sword into the ground, causing a shockwave to appear in the direction he's facing (like a Kaiser Wave).
The shockwaves keep coming one after the other, so it's hard to dodge.
Skillfully using a double jump, you can use the first jump to attack the large oni, and then use the second jump to dodge in between the shockwaves.
And most importantly, during this time, the large oni is standing still so if you use your special attack at this time, you'll easily defeat him.

The last boss of Akaiito, Nushi-sama.
When he gets attacked, he released a snake, so it's dangerous to attack when you're too close to him.
It's better to be farther away, just at the edge of your reach and jump attack and then run away.

At first, he only uses Pattern 1, but after receiving some damage, he'll move into Pattern 2, which is Lightning Mode. When he receives even more damage, he will repeatedly use Patterns 3 and 4.

Attack Pattern 1
Moves back and forth, ready to attack.
When Kei is within range, he'll reach out and make a short punch.
Or is it that he has a punch with a long reach? (The pixels are very rough so I can't tell).
Also, if you jump over Nushi, his attack will aim for the wrong side so you can counterattack.
Just be careful because once you hit Nushi, a snake will appear.

Attack Pattern 2
He's in a pose that looks as if he's chanting a spell and causes red lightning to strike.
Before and after he fires, he'll leave himself open, so you can target him then.

In addition, there are two types of lightning strikes.
There's one pattern where the lightning starts out at him and flies in all directions, and one where multiple shots are fired a Kei.
For the flying-in-all directions pattern, you can dodge by getting a bit of distance and ducking.
For the pattern where the lightning is targeting Kei, let the lightning get as close as possible before using a double jump to dodge.
Since the lightning targets the location where Kei is at, if you carelessly move up and down, it'll be difficult to dodge.
So you should try to stay on the ground unless you're dodging.

Since he stops moving for a long time as he's firing lightning, when he starts firing, there's a good chance to score a lot of hits by using your special attack since you don't have to worry about dodging the lightning either.

Attack Pattern 3
Teleports along the ground while throwing short and long punches.
This resembles Pattern 1, but since the punches are very precise...it feels like there are no openings.
It's not difficult compared to Pattern 2, so if you keep needling away at him while jumping to dodge, you should be able to win.

Attack Pattern 4
If Kei if hit by the flash of light, she'll be unable to move for a period of time.
This will even stop you if you're using your special move.
This doesn't seem to affect Kei if her back is to Nushi.
Since it takes some time after he adopts his stance to let loose the light, you should turn your back turning that time.

After you defeat Nushi, if you've collected all the hidden items, which are the Three Sacred Treasures, you'll have this encounter.
The hidden boss looks exactly like Kei (except the color is different).

At first, she'll use Pattern 1, but after receiving some damage, she'll move onto Pattern 2.
After you damage her even future, she'll also mix in Pattern 3.

In truth, she's really strong.
If you get even a little close, she'll slice at you.
There might be no other technique but to keep needling her when she shows a bit of an opening.
I can't think of any other tip than to drive her in a corner and use your special attack...

Attack Pattern 1
Like a mirror, she continues moving in the exact same fashion as the player.
Therefore, when you attack, Kei will also receive damage, but the enemy's attack is set lower than yours.
In addition, after receiving damage, you're invincible for a period of time so you can win just by attacking head on.

Attack Pattern 2
Repeatedly jumps and swings her sword.
When Kei approaches too close, she'll make a fast attack.
Because you have to deal with a counterattack if you head towards her face on, and her attack power is greater than yours, it's dangerous.
Since it seems that she's weak at fighting in the air, when she's in the air, you should also jump and attack in the air to damage her.
However, if you're close to her when you land, you'll receive a counterattack, so you should skillfully use a double jump to maintain some distance.
It seems there's no other choice but to use a hit-and-run strategy to slowly whittle away at her life.

Attack Pattern 3
Surrounded by a field of light, she rushes back forth along the ground.
It resembles Kei's special move, but she can use it 3 times in a row, plus there doesn't seem to be any limit on the number of times she can use it、
In addition, different from Kei's, hers doesn't make her completely invincible.
Because of that, if you also use your special attack, only you will be dealing damage and you can win.
You can also deal damage with your sword.
But since it's dangerous if you get too close, it's probably safer to concentrate on dodging.
Since the movements are simple and obvious, simply dodging should not be difficult.

For Those Who Just Can't Beat This

In truth, there is a hidden technique. When you're in the middle of a pose, enter ↑←→→↓↑↑
and all your stamina and spiritual energy will be restored.
In addition, you'll also be surrounded by ofuda.
You can only use this once per game though...

At the title, if you enter ↑←→→↓↑↑（you'll hear a SFX if successful), then you'll be able to play a hidden mode where you control Uduki.

The basic controls are the same except you don't have an awakening mode (you do have a special attack).
Also, the attack power of the enemies has increased so it's harder than the normal mode.

Of course, the bosses have also gotten stronger. The first stage boss summons more ordinary enemies.
The second stage boss has dead spirits from the moment the fight begins.
The third stage boss will toss out snakes even if you don't attack him.
That's the type of stuff that I've confirmed. You can use the same strategy as for the normal mode.
Cornering a boss and using your special attack is still effective so I think those that can clear the normal mode should be able to clear this mode with a little practice...
Even though I'm also not good at action games, I was able to beat this without using the "hidden technique".

Since the ending graphics are rather amusing, and are yuri in a way, I'd definitely recommend seeing them.

If you do certain actions during the game, you'll get bonus points.
Most importantly, it doesn't seem like there's a reward for having a high score, so it would only be if you were interested in it (or if you wanted to train your concentration)...
In addition, there might be other bonuses besides what is mentioned here, so it might be a good idea to search for them.

If you continually hit enemies (they don't have to be defeated), you'll get bonus points based on the number of hits.
The combo meter will be reset if Kei swings and misses or if she is damaged by an opponent.

However, if you have an ofuda barrier, the combo meter won't break even if you take damage.
In addition, you can use your special attack to rack up a combo in addition to normal attacks.
You can really rack up a combo if you have several enemies lined up.
When you're rushing forward, if you hit just one enemy, then the combo won't break so it's really effective.

If you devote yourself to defeating the enemies summoned by the first stage boss, if should be no problem to rack up a 50 hit combo.

If you can reach the boss without attacking (it's ok to use the "Cell Phone" item) and also without taking damage, you'll receive a bonus when attacking the boss.

During "Tea Time"（when items that increase your score drop from the sky),
if you manage not to pick up a single item at all, you will receive a bonus.
If you use your "awakening technique", then the speed of the items will slow down so it might be easier...?
Since the bonus will disappear if you gather even one, when you're surrounded by items, the risk of hitting one goes up.

It seems there is a bonus if you reach the boss without using your weapon and last until time runs out...
The source of this information comes from the fanbook, but since it rather troublesome to do this, I haven't confirmed it.