100% Quick Overview

[Holysword]

I'm writing this for people who just started playing the game and are aiming to perfect this game without replaying it over 9000 times like I did no ragrets. I found all information around needlessly confusing and none was complete.

Of course: spoilers ahead.

The tl;dr version is:
* plan for the "Walking Phonebook" achievement, you'll get most other achievements on the way
* you cannot get all endings in a single game, you'll have need at least 4 New Game+
* do not backup/copy/paste savegames for the Endings, you need to do all endings in one savegame for unlocking all phone numbers

The full version is - Game Overview and Hints:
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* Mission Types:
    * Attack [BOW ICON]: the default one
    * Item [FLASK ICON]: uninteresting
    * Defense [SHIELD ICON]: excellent for collecting phone numbers
    * DokiDoki [HEART ICON]: VERY IMPORTANT! These start the process of flagging for a specific ending
    * Versus [DEMON ICON]: some of those complete the flagging for specific endings

* About the missions:
    * Main Mission: progress story with Risu
        * [Attack, MANDATORY] I found some demons
        * [Attack, MANDATORY] HUGE demon detected
        * [Attack] A demon has appeared
        * [Versus] I'll take you the HELL on!
        * [Defense] I've got the perfect strategy!
        * [Attack] Demons discoverd!
        * [Item] I'm sensing...that demon?
        * [Versus] Gonna stomp the HELL out of you!
        * [DokiDoki] I'm not feeling well
        * [Versus] Kurona's Return
    * Side Missions: progress story with Chiru or Nanako (or the Kamizono sisters)
        * unlocked by progressing Events of each girl (shown as Exclamation Marks)
            * unlocked by feeding the girl:
                * use their favourite food: https://steamcommunity.com/sharedfiles/filedetails/?id=1454780928
                * the game says that "they love you plenty" once you fed them to the max
            * some events take a day to progress even if the girl is fed
        * Nanako Missions
            * [Attack] About Nanako-sama...
            * [Attack] Risu-san called me to the pool...
            * [Attack] Let's look for Kurona-san!
            * [Attack] Let's limbo!
            * [Defense] Kurona chan's got me!
            * [DokiDoki] Library investigation
            * [Versus] Farewell...
        * Chiru Missions
            * [Defense] Help me pick a present
            * [Attack] Found a crystal
            * [DokiDoki] "Going outside" practice
            * [Versus] School trip!
    * Free Missions: mostly for getting phone numbers; best to do the Defense Type (1-5 phone numbers per completion)
        * "A spooky SOS from a ghost~ Oooh~" is a "secret" Free Defense Mission. It is necessary to unlock the phone of Yuko Yureino" and hence, for the "Walking Phonebook" achievement. I'm not sure how often this quest appears, so maybe do it immediately when it pops.

* Flagging for the endings:
    * starts with DokiDoki Mission (Kamizono sister's don't count)
    * finishes after a specific Versus battle (usually)
    * the game only tells you that you are flagged for an ending when you are home
    * the Endings are:
        * Risu "Good" Ending
            * do the DokiDoki of Risu and nothing more.
        * Ending A - you'll "dedicate" to Chiru/Nanako only
            * do the DokiDoki mission of the chosen girl
            * unlock and do the Versus mission of the chosen girl
        * Ending B - you'll mix Risu with Chiru/Nanako.
            * do DokiDoki of Risu FIRST
            * do DokiDoki of the other girl
            * you will NOT unlock the girl's Versus mission
            * do the Kurona's Return mission
        * Harem Ending - a.k.a the correct ending
            * do DokiDoki of Risu FIRST
            * do DokiDoki of both other girls
            * wait for Kurona's Return mission to pop then IGNORE IT. Once Kurona's Return *disappears*, you unlocked the harem ending
    * you can get Risu's Good ending, continue playing and then get Nanako or Chiru's Ending B
    * after that you'll need 4 New Game+ to get all Phones/Endings
    * there is no need to farm for phone numbers in your first run. You'll get plenty of days when you won't have anything to do when you reach New Game+