Important thing to note gameplay wise is that you are WEAK the first time you play through the game. Though, it'll get significantly easier as you go on. I probably only spent 10+hours and 4 plays to get close to all the endings. Feel free to play through on the first go without too much reservations on meeting objectives to get a feel of the game. After viewing your first non-bad ending, you would have a choice to carry over some of your monsters to your next game. This might be kinda obvious, but in order to get to any character ending, you would need to be able to choose the character name under 'Marriage' - like this:
There are 3 'modes' which govern how much resources you would have initially, how many monsters you can carry over to your next game, and most importantly, the total game 'time' you have.
「ファーストモードã€→「ブラッドモードã€→「リ ュミスモードã€
'First Mode'->'Blood Mode'->'Lumis Mode'
*Actually, the names of the modes doesn't matter, neither does the names I reverse-romanised
What does matter is that you would want (if you'd want to) to advance your mode to the highest in the shortest amount of time so as to be able to reap maximum benefits(saves time too). The game is effectively a collecting and nurturing resources to collect even more resources in order to fulfill the requirements of your marriage within a set time.
The 3 modes:
'First Mode':
You are in this one if you are playing for the first time.
Playtime: Ends at １年４８週 - Year1 Week48 (each action takes up 1 week)
No. of monsters able to be carried over: 4 (i think)
To get into 'Blood Mode': Game ends and you view an ending (Bad End not included)(Yume/Fay/Rukuru endings recommended)
'Blood Mode':
Linear mode progression from 'First Mode'
Playtime: Ends at 2年４８週 - Year2 Week48 (each action takes up 1 week)
No. of monsters able to be carried over: 8 (i think)
To get into 'Lumis Mode': View リュミスＥＮＤ１ - Lumis Ending1
Requirement for Lumis Ending1: Wealth<5000, H<25, Splendor<40 + pick 'Lumis' from the 'Marriage' command
'Lumis Mode':
Linear mode progression from 'Blood Mode'
Playtime: Ends at 3年４８週 - Year3 Week48 (each action takes up 1 week)
No. of monsters able to be carried over: 15 (after you score full marks for the quiz that was unlocked after your first character ending)
*I do not remember the initial resources at each stage, but it should be obvious that they follow an increasing trend
I'll throw in these two guides I referred to as well:
http://moe.livedoor.biz/archives/3280470.html
http://www.geocities.jp/byougaku/suzukuri/suzukuri.htm
