I just finished playing through the game using the excellent achievement guides provided (here and here) and thought to condense the information so that people could go through the entire story and branches in two playthroughs and still experience all of the game with less repetition and gain 100% achievements. All information used in this guide is based on the creators of the two aforementioned guides.

The strategy is fairly simple. There are achievements tied to the 4 good endings and a number of bad endings, and some for more or less random actions along the way. I noticed that it is possible to build relationships with 3 out of 4 characters in one run, thus obtaining 3 good endings, and a lot of bad endings. Here, you will get most of the day-to-day achievements as well. Then, for the second run, you build relationship with the last character, obtaining the final bad endings and the few achievements we missed during branches on the first run.
For optional dialogue, there are often only two choices anyway, so you can alternate them between the two runs to get all of the story as well (most of it is exactly the same either way).

Prologue:
Kill both the maid and the guard to unlock Reckless Killing (1/22).

Day 1:
- Don't skip the induction introduction. (Mineko)
- Thank Mineko after the induction. (Mineko)
- I'd better go to the official lunch. (Utsuro)
- I'm a fan of combat strategy, too. (Utsuro)
(In the evening at the party you can obtain points with Hikari, but this is not the goal of the first playthrough: - Stay at the party and try to mingle. - I don't drink.)

Day 2:
- I’d like to try my hand at Poetry. (Mineko)
*Be good at poetry*:

• Relic of far hills
  
• Stones with unknown destiny
  
• Go; flow to your sea.

OR

• Thousands fight as one
  
• Banners speak fateful omen
  
• A red sky watches.

You will also unlock Impressive Poetry (2/22).

Day 3:
- History seems like an important subject. (Utsuro)
*Be good at history*

• C) One quarter
  
• B) 13
  
• A) His throne
  
• B) A servant in the kitchen
  
• A) In the garden

- I…I would love to. *Date with Utsuro on Friday* (Utsuro)

- Sure! It'll be fun! (Kaori)
- Why, what is your type? (Kaori)

When speaking with the maid in the evening:
- Have you heard about Hiro & Jiro?
You will unlock Spreading Rumours (3/22).

Day 4:
- Choose Tactics.
*Be good at Tactics*

• Send Archers on foot first.
  
• In the back of the retreat.
  
• To smash through enemy lines.
  
• Attacking the enemy from the sides rather than the front.
  
• Hit and run—inflict damage on a single target, then leave before they can retaliate. *Choice doesn't matter*

You will unlock Asumi the Swot (4/22).

When speaking with Ms. Nagai, select "Thanks for the heads up." (in order to unlock Seduce and Drug later on this playthrough.)

Day 5:
- Edo Politics may be useful. (Mineko & Utsuro).
- The Lord Regent should have the power. (Side with Mineko).
- He will bring order and purpose to the Justicars. (Mineko).

SAVE before the date with Utsuro.

- Cancel the date with Utsuro and stay with Kaori. (She will take you out instead).
- Let's just say, they weren't my type.
You should unlock kissing scene and Kaori Suggestion (5/22).

LOAD the save from before the date.

- Meet with Utsuro for the Date. (Utsuro)
- A handsome guy like you? Of course I would! (Utsuro)
- It’s absolutely beautiful! (Utsuro)
- Keep your hand there (Utsuro)
- Not at all… (Utsuro)

Proceed with the playthrough in which you went on the date with Utsuro (in other words, we do not save progression with Kaori. We will still be able to romance her later.)

Day 6:
- Hit the Beach (Mineko)
- But I do want to know. (Mineko)
- What about me…? (Mineko)
Kissing scene occurs.

Day 7:
In the evening, when confronting the principal:
- Disable the principal. You will unlock Seduce and Drug (6/22) only if you had selected "Thanks for the heads up" during the Day 4 conversation.

Day 8:
- Meditation (Mineko)
- I need to take the time to clear my mind. (Mineko)

Evening conversation with Kami:
- Mineko (Mineko)

Day 9:
Do what you like.

Day 10:
At swimming with armour:
- Alright, quick before Mr Furuya forces me to jump. (Kaori)
You will unlock Try Cosplay (7/22).

Day 11:
Win against the assassins:

• Climb the nearest tree and hop across
  
• Military-crawl through the grass
  
• Shoot a tranquillizer dart at him

Kill the assassins. You will unlock The True Assassin (8/22).

At evening, select to accompany:
- Hikari

Day 12:
- Join Kaori for a swim. (Kaori)

Day 13:
MAIN SAVE POINT. SAVE!
If you followed the guide until now you should be able to romance all three characters.

- Confess to Mineko
- Select Utsuro as target (omitting this step unlocks True Justicar ending instead)
- Select Keiji as target
- Kill Keiji
- Kill Sen
You will unlock Completed the Game (9/22) and True Love #3 (10/22).

LOAD FROM MAIN SAVE POINT

- Confess to Utsuro
- Select Keiji as target
- Kill Keiji
- Kill Sen
You will unlock True Love #2 (11/22).

LOAD FROM MAIN SAVE POINT

- Confess to Kaori
- Select Keiji as target
- Kill Keiji
- Kill Sen
You will unlock True Love #4 (12/22).

LOAD FROM MAIN SAVE POINT

- Confess to Hikari
You will unlock Hikari's Unrequited Love (13/22).

LOAD FROM MAIN SAVE POINT

- Confess to either Mineko, Utsuro or Kaori
- Select Hikari as target
You will unlock Death of Hikari (14/22).

LOAD FROM MAIN SAVE POINT
- Confess to either Mineko, Utsuro or Kaori
- Select Keiji as target
- Disable Keiji
- Select 'Try to get to his throat'
You will unlock Mercy is for the Weak (15/22).

LOAD FROM MAIN SAVE POINT
- Confess to either Mineko, Utsuro or Kaori
- Select Keiji as target
- Kill Keiji
- Disable Sen
- Tackle Sen from behind
You will unlock Dying Alone (16/22).

LOAD FROM MAIN SAVE POINT

- Confess to either Utsuro or Kaori
- Select Mineko as target
You will unlock Mineko Falls (17/22).

End of first playthrough.

Almost done! Only a few achievements left to go. The second playthrough focuses entirely on the Hikari route, which also prevents us from accidentally spending time with other characters (this guy seriously needs attention!)

Important! Do not gain relationship with Mineko, or you cannot kill Utsuro in the end (for the achievement). Just avoid her as much as possible on the free days.

Prologue: Do what you like.

Day 1:
- Skip the induction introduction.
You will unlock Skipping the Intro (18/22).

- Stay at the party and try to mingle.
- I don't drink.

Day 2:
- I might as well go for Physical Training.
- Go all out!
- Medium pace.
- Medium pace.
You will unlock Obstacle Course (19/22).

Day 3:
- Jujutsu would be useful.
- Ask Hikari to partner up.
- Dodge the first blow to put him off balance.
- Perform a low kick and aim for his legs
- Adjust your footing to land a blow on his instep.
- Send a blow between his shoulder blades
- Ask Hikari out on Friday. *There is a 2nd chance for the date later, so you can actually choose for yourself.*

Day 4:
Do what you like.

Day 5:
- Horsemanship could be fun.
- Take control of the horse yourself
- Really, but you sure you wouldn't rather stay?
- Yes *If you didn't ask for a date on day 3*
- Meet with Hikari for the Date.
- I’d invite a handsome guy like you anywhere.
- Keep your hand there

Day 6:
- Relax in the Dorm
- I like you, too.

Day 7:
Do what you like.

Day 8:
During conversation with Kami:
- Hikari

Day 9-10:
Do what you like.

Day 11:
At evening, select to accompany:
- Hikari
- Kiss him

Day 12:
Do what you like.

Day 13:
MAIN SAVE POINT. SAVE!

- Confess to Mineko
- Select Utsuro as target
You will unlock Utsuro falls (20/22).

LOAD FROM MAIN SAVE POINT

- Confess to Hikari
- Select Keiji as target
- Kill Keiji
- Kill Sen
You will unlock True Love #1 (21/22).

LOAD FROM MAIN SAVE POINT

- Confess to Hikari
- Select Keiji as target
- Disable Keiji
- Kill Sen
You will unlock The True Justicar (22/22).

Congratulations, you have 100%'ed the game!