Effects of Shiori's birthday (WIP)

After asking the player to enter their own name, date of birth, and blood type, Tokimeki Memorial: Forever With You takes the perhaps unusual step of asking you to select classmate Fujisaki Shiori’s date of birth and blood type as well. This has several mechanical effects.

1. Invalid dates
2. Club
3. Same birthday check
4. Other

Invalid dates

You can’t set either the player or Shiori’s birthday to Feb 29. While 1996 is a leap year, the game won’t let you select that. Perhaps the developers thought it would be unfair to have one birthday in the entire game.

Naturally, you can’t set either birthday to invalid dates (Feb 30, Feb 31, Apr 31, Jun 31, Sep 31, or Nov 31). If you try, it will automatically set it to the last valid day of that month.

Club

Shiori’s birthday determines which club she will join. This feature was already well known, with the exact formula even appearing in English in QLai’s FAQ v1.2 as far back as 13 December 1996.

The particular code appears in exedir/name_ext.exn:

uVar3 = (((birthday_shiori << 0x17) >> 0x1b) * 3 + (birthday_shiori & 0xf)) % 0xb;
club_800ee92a = (byte)(uVar3 << 4) | club_800ee92a & 0xf;
printf("FUJISAKI CLUB %x\n",uVar3);
bVar1 = (&DAT_name_ext__8014d03c)
        [((uint)(birthday_player << 0x15) >> 0x1e) * 4 + ((birthday_shiori << 0x15) >> 0x1e)];
printf("aisyo %d \n");

A side-effect is that there is a slightly uneven distribution of which club Shiori will join. There are 32 days which will cause Shiori to join the drama and swimming club (8.77% each), 33 days to join the art, brass band, computer, literature, or soccer club (9.04% each) and 34 days on which she will join the baseball, basketball, science or tennis club (9.32% each).

Note the unusual way birthdates are stored. It would be easy to store the day and month in separate bytes, but instead they’re stored in one half byte each. Shiori’s default birthday of 14 Feb is stored as 0xE2, or binary 0b11100010, split into 0b1110 (14) and 0b0010 (2). Of course, since four bits have only 16 possible values, days above 15 result in an overflow of 01 to the next byte (PSX CPU is MIPS little-endian). Note how the calculation in line 1 works by shifting 23 bits left to cut off all but the top eight bits, then shifting 27 right to cut off the bottom four bits.

The particular calculation can be simplified to (month + (3 * day)) mod 11, as correctly stated in QLai’s 1996 FAQ. Interestingly, QLai states that the PC Engine version places the date and month the opposite way around in the calculation; I wonder if this swap is a bug or intentional.

Note also the use of printf statements; these are normally never seen when playing on an actual PlayStation, but you can see them in the debug output of an emulator.

For players, if you want Shiori to join a specific club, the complete list of dates of birth to select for Shiori is as follows:

Art

Jan: 1, 12, 23

Feb: 8, 19

Mar: 4, 15, 26

Apr: 11, 22

May: 7, 18, 29

Jun: 3, 14, 25

Jul: 10, 21

Aug: 6, 17, 28

Sep: 2, 13, 24

Oct: 9, 20, 31

Nov: 5, 16, 27

Dec: 1, 12, 23

Baseball

Jan: 9, 20, 31

Feb: 5, 16, 27

Mar: 1, 12, 23

Apr: 8, 19, 30

May: 4, 15, 26

Jun: 11, 22

Jul: 7, 18, 29

Aug: 3, 14, 25

Sep: 10, 21

Oct: 6, 17, 28

Nov: 2, 13, 24

Dec: 9, 20, 31

Basketball

Jan: 3, 14, 25

Feb: 10, 21

Mar: 6, 17, 28

Apr: 2, 13, 24

May: 9, 20, 31

Jun: 5, 16, 27

Jul: 1, 12, 23

Aug: 8, 19, 30

Sep: 4, 15, 26

Oct: 11, 22

Nov: 7, 18, 29

Dec: 3, 14, 25

Brass band

Jan: 5, 16, 27

Feb: 1, 12, 23

Mar: 8, 19, 30

Apr: 4, 15, 26

May: 11, 22

Jun: 7, 18, 29

Jul: 3, 14, 25

Aug: 10, 21

Sep: 6, 17, 28

Oct: 2, 13, 24

Nov: 9, 20

Dec: 5, 16, 27

Computer

Jan: 8, 19, 30

Feb: 4, 15, 26

Mar: 11, 22

Apr: 7, 18, 29

May: 3, 14, 25

Jun: 10, 21

Jul: 6, 17, 28

Aug: 2, 13, 24

Sep: 9, 20

Oct: 5, 16, 27

Nov: 1, 12, 23

Dec: 8, 19, 30

Drama

Jan: 11, 22

Feb: 7, 18

Mar: 3, 14, 25

Apr: 10, 21

May: 6, 17, 28

Jun: 2, 13, 24

Jul: 9, 20, 31

Aug: 5, 16, 27

Sep: 1, 12, 23

Oct: 8, 19, 30

Nov: 4, 15, 26

Dec: 11, 22

Literature

Jan: 7, 18, 29

Feb: 3, 14, 25

Mar: 10, 21

Apr: 6, 17, 28

May: 2, 13, 24

Jun: 9, 20

Jul: 5, 16, 27

Aug: 1, 12, 23

Sep: 8, 19, 30

Oct: 4, 15, 26

Nov: 11, 22

Dec: 7, 18, 29

Science

Jan: 4, 15, 26

Feb: 11, 22

Mar: 7, 18, 29

Apr: 3, 14, 25

May: 10, 21

Jun: 6, 17, 28

Jul: 2, 13, 24

Aug: 9, 20, 31

Sep: 5, 16, 27

Oct: 1, 12, 23

Nov: 8, 19, 30

Dec: 4, 15, 26

Soccer

Jan: 2, 13, 24

Feb: 9, 20

Mar: 5, 16, 27

Apr: 1, 12, 23

May: 8, 19, 30

Jun: 4, 15, 26

Jul: 11, 22

Aug: 7, 18, 29

Sep: 3, 14, 25

Oct: 10, 21

Nov: 6, 17, 28

Dec: 2, 13, 24

Swimming

Jan: 10, 21

Feb: 6, 17, 28

Mar: 2, 13, 24

Apr: 9, 20

May: 5, 16, 27

Jun: 1, 12, 23

Jul: 8, 19, 30

Aug: 4, 15, 26

Sep: 11, 22

Oct: 7, 18, 29

Nov: 3, 14, 25

Dec: 10, 21

Tennis

Jan: 6, 17, 28

Feb: 2, 13, 24

Mar: 9, 20, 31

Apr: 5, 16, 27

May: 1, 12, 23

Jun: 8, 19, 30

Jul: 4, 15, 26

Aug: 11, 22

Sep: 7, 18, 29

Oct: 3, 14, 25

Nov: 10, 21

Dec: 6, 17, 28

Same birthday check

The game actually checks if the player and Shiori have the same birthday. This was widely known even at the time, since there’s a unique birthday event. Of course, since the player and Shiori are osananajimi, if they had the same birthday then they would have shared birthday events in the past.

Still, here’s the relevant code from the main game executable:

undefined4 fujisaki_2nin_birth_check(void){
  undefined4 result;
  int iVar1;
  uint uVar2;
  undefined auStack52 [32];
  undefined auStack20 [20];
  
  get_grp(auStack20,auStack52);
  if (((birthday_player & 0xf) == (birthday_shiori & 0xf)) &&
     ((birthday_player << 0x17) >> 0x1b == (birthday_shiori << 0x17) >> 0x1b)) {
    if ((current_month == '\x03') || ((current_month == '\x04' && (current_day < 4)))) {
      iVar1 = reserved_date(current_year,current_month,current_day);
      if (iVar1 < 1) {
        iVar1 = birth_day_check(0xf); // 0xf = player
        if (iVar1 == 1) {
          uVar2 = get_g_zyotai_s(0);  // 0 = shiori
          result = 0;
          if ((uVar2 & 0x80) != 0) {
            result = 1;
          }
        }
        else {
          result = 0;
        }
      }
      else {
        result = 0;
      }
    }
    else {
      result = 0;
    }
  }
  else {
    result = 0;
  }
  return result;
}

Several of these function names are pulled from exedir/o.bin, a leftover object file. This means the game’s developers called this function fujisaki_2nin_birth_check, where “2nin” probably means 「二人」, meaning two people or a couple, more commonly read “futari”. The function names get_grp, reserved_date, birth_day_check and get_g_zyotai_s are also from the object file.

The check is only passed if:

1. Shiori and the player have the same birth month
2. Shiori and the player have the same birth day
3. The current day is between Mar 1 and Apr 3 inclusive
4. You don’t have a date scheduled today
5. It is currently the player’s birthday
6. Bit 7 of get_g_zyotai_s for Shiori is set (todo: determine significance of this function)

Other

There are other references to Shiori’s birthday which I’ve yet to decode.