you start off with little sister.  head to school
equipping passive skill may drop potion would help right from the start

to equip passive skills, press the "Q" button, then choose the first option. If you're alone, you will get a question prompt, choose the first option. If you're with your sister, it will give you 3 options. Option 1 - equip passive skill on younger sister. Option 2 - equip passive skill on older sister. Option 3 - go back. You will then be given the question prompt, choose the first option. You will then be given 4 options. Option 1 - Cancel, Option 2 - Passive skill(1/3/5), Option 3 - Passive skill(2/4/6) and Option 4 (Next Page/Go back to first page). Once you've selected the maximum equippable 
skills, you will be given a question prompt, choose the first option. To check if you got it right, go to the char's skill menu, and the equipped passive skills will be listed there.

Nao (sister with short hair):
First - Recover MP after you win a battle (Rio must also have this set to have an effect) *you start off with this skill
Second - May find a potion after winning a battle *you start off with this skill
Third - Easier to get raped *keep getting raped during battles. will automatically learn after leaving a town
Fourth - Agi up at the start of the battle for 3 turns 
Fifth - Addicted to sperm (mobs always cums inside) *keep getting cummed inside. both events/battle rape works. will automatically learn after leaving a town
Sixth - Recover more MP during battle (Rio must also have this set to have an effect) *you get this after getting the second sisters kissing event

Rio (sister with long hair):
First - Recover MP after you win a battle (Nao must also have this set to have an effect) *you start off with this
Second - Rio will have atk up at the start of the battle for the first turn *you start off with this
Third - Easier to get raped *keep getting raped during battles. will automatically learn after leaving a town
Fourth - Nao will have atk up at the start of the battle for the first turn
Fifth - Addicted to sperm (mobs always cums inside) *keep getting cummed inside. both events/battle rape works. will automatically learn after leaving a town
Sixth - Recover more MP during battle (Nao must also have this set to have an effect) *you get this after getting the second sisters kissing event

get to second floor and kill boss. no scene if you lose
go to the very west and meet up with your sister
exit town
equip other sister with passive skill

/optional1
head east and enter the town east of the starting town
head east and enter the house with the red roof at the south part of town
talk to the npc and he will offer you freelodging with dinner. there's an hscene if you accept. can come back 2 more times for more scenes
enter the house at the ne most part of town.
you can donate 1k, and will eventually get an elixir after donating a significant amount.
/endoptional1

head west and enter the forest
follow the path and will take you to the exit
head north and enter town

/optional2
at the nw part of town, behind the house with the green roof is a shady guy that will buy your underwear for 1k each. this can be exploited as you can always get a new pair at your house, in the closet inside the bathroom. sell one of the sister's underwear, switch to other sister, sell her's, teleport home using teleport item, grab new pair for each sister then teleport back using the carriage guy at the west end of the starter town. that's a net gain of 1750 gold each trip. if you even want to go further ahead with the exploit, get atleast 16400 gold, try to get to the third town, and buy the strongest weapons and accessory at the weapon shop. then you can even go to the extreme, and buy stat increasing items in the third town. go to the ne end of the town and enter the barracks.  head to the second floor and go to the very sw end. it will be the npc with blonde hair and green clothes. each stat increasing item costs 10k, so it will be quite a grind
/endoptional2

go west/nw and enter the house with the green roof
talk to the npc by the table
go to the inn
talk to the npc inside the north middle room
exit town and go back to the previous forest

/optional3
you can head back to the starting town and talk to the htrainer for the short haired sister. he is located in the house next to the sisters' to the east. talk to him and he blackmails her. after the event she can now start learning skills from the htrainer in exchange for her "obedience". to learn skills you will need ap points. you get 10 ap points per level, 3 ap points per in battle rape, and 1 ap point if the raper cums inside her. skills you can learn:
1-1 remove ailments from character
1-2 restores a small amount of hp to both sisters
2-1 raise the defense of one sister
2-2 raise the defense of both sisters
3-1 fire damage to all enemies
3-2 makes mob use hattacks more frequently. hits all enemies

after completing the first 6 skills you gain access to another set of skills
4-1 restores a moderate amount of hp to both sisters
4-2 increased magic defense of both sisters
4-3 able to get pregnant passive trait
/endoptional3

from the forest north entrance, follow the path until the path curves to the east
enter a grassy route heading south instead
turn east immediately when you can and keep heading east
the flower you need will be near the dead end
head back to the npc in the inn and give him the flower
after that, npc says he needs another one. you could either buy one for 10k from the npc, or get one from an npc in town inside the se most house using the long haired sister.
if you decide to get it for free, talk to the npc with the long haired sister and he would offer to give the flower if he in returns help "heal" him. talk to the npc again after you cure the little girl and it would initiate hevent. after the event, the long haired sister can now start learning skills from the htrainer. skills you can learn:
1-1 restore a small amount of hp to one sister
1-2 revive short haired sister
2-1 raise the attack of one sister
2-2 raise the attack of both sisters
3-1 damage one target
3-2 damage the mp of one target

after completing the first 6 skills you gain access to another set of skills
4-1 restores a greater amount of hp to one sister
4-2 restores great amount of hp on both sisters and revives short haired sister if incapacitated
4-3 able to get pregnant passive trait

talk again to the npc in the inn and he will make a cure
talk to the npc inside the green roof house again and he will reward you with a "low stone"
use it to increase your passive skill capacity by one.
now is a good time to do /optional3 if you haven't yet
exit town
equip more passive skills and head straight north
explore the area and you should come across a wood cabin
enter and you'll end up fighting the purple haired girl
you must beat her to progress the story. losing has no hscene
after defeating her, the sisters learn very valuable new skills
short haired sister learns a single target attack that can cause agi down, def down and can stun the target. long haired girl learns a single target attack that can paralyze, poison, confuse, blind and sleep the target.

/optional4
exit the forest from where you entered and head west/nw
explore area till you get to another zone
kill bandit leader guarding the chest. inside the chest is another low stone
having one of the sisters raped in battle, then losing the battle after will give an hscene for that raped sister. if both gets rape during battle, you will get both of the sisters' hscene.
/endoptional4

/optional5
head back to the first town and enter the house at the very nw part of town
talk to the npc inside
now head back to the forest you fought the purple haired girl and take the north exit
/endoptional5

head north till you reach the third town and enter

/optional6
head to the pub ne of town
talk to the bartender
choose the option for 1k
now the item shop will sell an item that increases horniness by 30 points
/endoptional6

/optional7
zone in the nw most exit of town
head nw and you'll end up fighting a group of 8 mobs
lose and you get an hscene, win and you get nothing
/endoptional7

/optional8
to the west of the third town, there will be a bridge, and crossing that, you'll notice a mob moving around at a very fast pace. catch and kill this mob. he's fairly tough, but he drops an accessory which i think is the best accessory in the game. it gives +5 atk, +5 def and regenerates some hp after each turn. might take awhile, but try to get 2 of these accessory. losing does not give a new scene
/endoptional8

/optional9
from the 3rd town, go south a bit, passed the putruding body of water, then head east
enter the forest
explore until you get to a dead end at the ne portion of the 2nd zone
fight initiates and you must win this fight to progress
no hscene if you lose
after the battle, both sisters will learn an all target attack version of their status-effect inducing move and their 4th slot passive skills. don't foreget to equip
head back to the first town and head to nw house
talk to npc
head to third town
enter the house behind the tool shop
talk to npc, choose 3rd option
you will get the sisters kissing scene when you exit the house. you now have the option of kissing the other sister when you talk to her
head back to first town
enter nw house and talk to npc
after the event reenter the house,and you will get a scene
after the scene, you receive another low stone, and both sisters learn their 6th slot passive skill. don't forget to equip
you can now have sex with the other sister in the comfort of their home
/endoptional9

/optional10
past the bridge to the west, head more w/nw
enter the tower
explore the tower and flip 2 switches in total to gain access to boss
kill boss and you get access to a chest containing another low stone
getting raped in battle with boss then losing will give you an hscene of the raped sister(s)
/endoptional10

exit the 3rd town from the north exit
follow the linear path to a cave

/optional11
it may be a good idea to farm the swordman in the first area, and the fire lady enemy in the second area. they drop the strongest sword and the strongest spear in the game respectively.
/endoptional12

explore until your reach the purple haired girl
fight initiates and you must win to progress. no new scene if you lose. this is technically the last boss and has 2 forms. if you lose to the 2nd form, you will have to fight the first form again when you fight her again.
she drops a dog collar after the fight

after the scene, you find yourself back in the starter town. the plot is over, so you can go after the optional stuff, hunt for hscene, and go for extra dungeon

the extra dungeon can be accessed in the starter town, in the most nw building, door in the left nothing really special in the mobs here, other than possibly dropping stat-increasing items, same ones you can buy from npc
extra dungeon boss is just a bit stronger version of the last boss, and has a possibility of dropping a dog collar. to get all the hscenes, you will need 2 dog collars

after learning all of the skills from both sisters htrainers, switch to the long haired sister and zone into her htrainer's house. she will discover her htrainer isn't there. head back to the starter town and go to short haired sister's htrainer using the long haired sister. an event initiates. after the scene, you now have:
1 - access to the hcg viewer in the computer in your house
2 - new sex options open up for the sisters' htrainers
3 - the sisters can now have sex with the other's htrainer

after getting all the hscenes, all 6 passive skills and having atleast 700 nastiness, equip both sisters with the dog collar then zone into the short haired htrainer's house. you should get the dog collar event. if not, you may need to do the gangbang scene about 2+ more times

hcg in the computer
1 - 1 (learn 1 - 1 skill from short haired sister's htrainer)
1 - 2 (learn 3 - 1 skill from short haired sister's htrainer)
1 - 3 (talk to the short haired htrainer and accept his training)
1 - 4 (naked walk option after getting the gangbang hscene from the htrainers)
1 - 5 (talk to the htrainer after completing the first 6 skills)
1 - 6 (talk to the long haired sister's htrainer while using the short haired sister after the gangbang scene)
1 - 7 (get only the short haired sister raped in a non-boss zone/battle, then lose the fight)
2 - 1 (once you can completely strip, enter the men's washroom naked while using the short haired sister and choose the first option. you may have to talk to the npc walking around the washroom area beforehand)
2 - 2 (get the short haired sister raped in battle while fighting the bandit boss, then lose the fight)
2 - 3 (get the short haired sister raped in battle while fighting the snake boss, then lose the fight)
2 - 4 (accept the npc's offer for free lodging/dinner in the first town)
2 - 5 (complete and last 3 skills from the htrainer)
2 - 6 (gotten from dog collar event)
3 - 1 (accept to heal the htrainer in exchange for the grass)
3 - 2 (learn 1 - 1 skill from long haired sister's htrainer)
3 - 3 (video sex option after getting the gangbang hscene from the htrainers)
3 - 4 (learn 2 - 1 skill from long haired sister's htrainer)
3 - 5 (talk to htrainer after completing the first 6 skills)
3 - 6 (talk to the short haired sister's htrainer while using the long haired sister after the gangbang scene)
3 - 7 (get only the long haired sister raped in a non-boss zone/battle, then lose the fight)
4 - 1 (once you can completely strip, enter the men's washroom naked using the long haired sister and choose the first option. you may have to talk to the npc walking around the washroom area beforehand)
4 - 2 (get the long haired sister raped in battle while fighting the bandit boss, then lose the fight)
4 - 3 (get the long haired sister raped in battle while fighting the snake boss, then lose the fight)
4 - 4 (accept the npc's offer for free lodging/dinner in the first town)
4 - 5 (gotten from dog collar event)
5 - 1 (gotten from gangbang scene)
5 - 2 (last sex option from long haired sister's htrainer after getting the gangbang scene)
5 - 3 (gotten from first sisters kissing scene)
5 - 4 (talk to the other sister in your house after the 2nd sisters kissing scene and choose to have sex)
5 - 5 (have both sisters get raped in a non-boss zone/battle then lose)
5 - 6 (lose to the 8 mob battle in the 3rd town)

misc notes
-it is possible to finish the game without interacting with the htrainers. you don't get anything special by protecting your chastity, so no point doing it
-you can actually get the men's washroom right at the start of the game. talk to the npc roaming around the washroom stalls, stand right in front of the men's washroom, strip and as you exit the menu immediately enter the men's washroom and choose first option.
-hope you found this walkthrough helpful and enjoy

X3R3X