I spent ages trying to collect the Pickup Legend achievement for sleeping with all the girls within 18 days, and as I played I made a note of every single date, just in case I succeeded and could share the info. So, this is my complete route to the Pickup Legend achievement, girl by girl, including when to unlock secret characters. I'll start with a few tips to make it as easy as possible.

PLEASE NOTE! This playthrough which gave me the achievement had Momo unlocked on Day 1. I only recommend following my guide if you see the BAG OF GOLDFISH in-store on the Huniebee when Kyu first gives it to you, and then throwing the fish in the trash outside on what will be your third date of the game, with Tiffany. If you start a game where fish are not available on Day 1, there is no guarantee when you will be able to buy them, and I cannot advise accurately for the achievement.

- Play the game on the easy setting. It takes longer for the dates to become really hard that way.

- The visit order of girls on Day 1 will enable you to visit with nine girls on the first day, but this is the only day this will happen. Every other day will have 4 dates, until you start sleeping with the girls and then you will mostly have 3 dates per day, as the girls take up your morning slot when you take them home, meaning your first date of the day will be afternoon. I pursued Beli and Lola early on, as they often go out of town.

- Give the girls alcohol whenever possible, so you start as many dates as you can with sentiment for date gifts. Most girls will only take alcohol in the evening or at night, and only indoors in some locations, but there are exceptions. I believe Jessie, Momo and Audrey will drink anywhere any time, and Aiko will drink outside as well as in if it's the evening or night. Momo will also drink in your bedroom. Venus needs far more alcohol than all the others to be affected.

- YOU MUSTN'T FAIL ANY DATES, so I strongly recommend playing the game in WINDOWED mode, it makes shutting down the game much faster and easier when you get the 'fail' message. Do not let the game save if you fail a date!

- Make sure you buy gifts and talk to the girls, you need as much Hunie as possible to upgrade your traits to make success easier. Also, girls can't go on dates if they don't have 2 bars in their hunger meter, so before a date, make sure you don't talk to them to the point they have an empty hunger meter, or wind up without any food items left to buy (or no Munie to buy them), as you will have to close and reload your game to start again with that girl. Don't throw away your tissues or magazine because you will need to give them to Kyu on day 5.

- Several times during my game, I had to visit girls just to bide time throughout the day before a 'sex date' with another girl. When that happens I will write NO DATE after her name; you can go on a date if you really want to, but it's best not to when you don't have to, so the date difficulty doesn't climb. I will write SEX DATE on the night dates where you will take the girls home.

--------------------------------------------------------

DAY 1 (BUY FISH!)

First date: Audrey (choose the shopping mall as your first location)
Second date: Kyanna
Third date: Tiffany (THROW AWAY THE FISH when your date with Tiffany is over, before you try to leave her. Momo will appear when you try to leave, it doesn't really matter which girl you select from the Huniebee to try and go to.)
Fourth date: Momo
Fifth date: Aiko
Sixth date: Beli
Seventh date: Jessie
Eighth date: Lola
Ninth date: Nikki
-----
DAY 2

First date: Beli
Second date: Tiffany
Third date: Audrey
Fourth date: Jessie
-----
DAY 3

First date: Lola
Second date: Tiffany
Third date: Beli
Fourth date: Audrey
-----
DAY 4

First date: Lola
Second date: Kyanna
Third date: Aiko
Fourth date: Beli (SEX DATE)
-----
DAY 5 (KYU UNLOCKS)

Beli will still be there in the morning, and once you try to leave (again, it doesn't matter who you try to go to) Kyu will appear to congratulate you on your lost virginity, and she will be added to the Huniebee. You can then take her on the first date of the day. Don't forget to give her your BOX OF TISSUES and your DIRTY MAGAZINE; she gives you a plushie and the 'WEIRD THING' which is needed later for unlocking Celest.

First date: Kyu
Second date: Jessie
Third date: Kyanna
Fourth date: Tiffany (SEX DATE)
-----
DAY 6 (You will mostly have 3 dates per day from here, since each bedded girl stays all morning.)

First date: Aiko
Second date: Kyu
Third date: Lola (SEX DATE)
-----
DAY 7

First date: Momo
Second date: Nikki
Third date: Jessie (SEX DATE)
-----
DAY 8

First date: Kyu
Second date: Nikki
Third date: Aiko (SEX DATE)
-----
DAY 9

First date: Kyanna (NO DATE)
Second date: Momo
Third date: Kyu (SEX DATE)
-----
DAY 10 (UNLOCK CELEST. This is a free day of no dates, and no sex date, as you must unlock Celest on the beach at night. Nikki will be the one on the beach at night; DO NOT TAKE HER ON A DATE, if you succeed it will become a sex date and Celest won't unlock. There is no guarantee when someone will be on the beach at night again.) You will only be able to date Celest in the evening and at night, she is asleep in the mornings and afternoons.

First date: Lola (NO DATE)
Second date: Beli (NO DATE)
Third date: Nikki (NO DATE - try to give her the WEIRD THING, which she rejects, and then try to leave by selecting any girl on the Huniebee, it doesn't matter which. Celest will appear and ask for the WEIRD THING, you can then take her on a date.
Fourth date: Celest
-----
DAY 11

First date: Kyu (NO DATE)
Second date: Tiffany (NO DATE)
Third date: Celest
Fourth date: Nikki (SEX DATE)
-----
DAY 12

First date: Aiko (NO DATE)
Second date: Celest
Third date: Audrey (SEX DATE)
-----
DAY 13

First date: Tiffany (NO DATE)
Second date: Jessie (NO DATE)
Third date: Kyanna (SEX DATE)
-----
DAY 14 (VENUS UNLOCKS)

Once you try to leave Kyanna (once again, it doesn't matter which girl you try to go to) Venus will show up. She will talk to Kyu and then you, and be added to the Huniebee. You can then take her for a date.
First date: Venus
Second date: Kyu (NO DATE)
Third date: Nikki (NO DATE)
Fourth date: Momo (SEX DATE)
-----
DAY 15

First date: Venus
Second date: Beli (NO DATE)
Third date: Celest (SEX DATE)
-----
DAY 16

First date: Venus
Second date: Kyu (NO DATE)
Third date: Momo (NO DATE)
-----
DAY 17 (FINAL DAY. You will sleep with Venus on the night date.)

First date: Jessie (NO DATE)
Second date: Kyanna (NO DATE)
Third date: Audrey (NO DATE)
Fourth date: Venus (SEX DATE)
-----

This should earn you the Pickup Legend achievement. I apologise for the long-winded guide, I just wanted to try and make it as helpful and accurate as possible. I hope it helps others get this rather tricky achievement. Please consider rating my guide if you use it. :-)