Yoshika Revival Bug

Specifications

• Versions: 1.00a - 1.00b - 1.00c
• Difficulty: Easy - Normal - Hard - Lunatic - Extra - Overdrive
• Mode: Main game - Practice mode - Spell practice
• Shottype: Reimu - Marisa - Sanae - Youmu

What happens

Sometimes when Yoshika is dead, she will not be revived by Seiga: Seiga continues to shoot bullets as if Yoshika is still alive. This behaviour only happens on the first two spell cards of Seiga regardless of difficulty. Additionally, this behaviour is most commonly encountered in practice mode (especially using practice tools), but it is also possible to encounter this issue in a real run.

How it happens

While the cause of this bug is the same on both the first spell-card and second spell-card, the set-ups are slightly different:

Spell 1

1. On this stage, reset while Yoshika is alive on any of the following sections:
   • 240 frames after Seiga's first spell started.
   • 160 frames after Seiga's second spell started.
   • During Seiga's third non-spell started.
   • 160 frames after Seiga's third spell started.
2. Then reset the stage by doing Esc + R. DO NOT restart the stage from the main menu, but do it from the pause menu instead.
3. Reach Seiga's first spell and kill Yoshika within the first 240 frames of this spell-card.

Note that this bug works with replays too. This means that if you have a functional Stage 4 replay that finishes Seiga's first spell within 240 frames, it's possible to encounter this bug when you restart the stage from the pause menu. By restarting, the replay desyncs on Seiga's first spell, but this can easily be fixed by going back to the main menu and replaying the replay.

Spell 2

1. On Seiga's first spell, finish the spell-card while Yoshika is still alive.
2. Within the first 160 frames of Seiga's second spell, kill Yoshika.

Unlike the bug with the first spell-card, this bug does not involve resetting the stage, meaning you can have a full game replay that encounters this issue.

Why it happens

Global variables

The game uses global variables (e.g. GI0, GI1, GI2, GI3) for certain patterns. When a stage is loaded, every global variable's value is set to 0. Here's an example of how the initialisation would look for every global integer variable:

GI0 = 0;
GI1 = 0;
GI2 = 0;
GI3 = 0;

This global variable initialisation is done every time a new stage is loaded into the memory, which is when you load a stage through either a stage transition or from the main menu. Note that this initialisation is not done when you reload the stage by e.g. Esc + R. For our interest, this issue is related to how global variable GI1 is accessed and written to by the game's code.

In the context of this bug, only the global variable GI1 is used. This global variable GI1 can have two values in this stage:

1. GI1 = 0, which is the state when Yoshika is dead on attacks Spell 1, Spell 2, Non-spell 3, and Spell 3
2. GI1 = 1, which is the state when Yoshika is alive on attacks Spell 1, Spell 2, Non-spell 3, and Spell 3

This variable is used by Seiga, who will proceed to do a different action depending on the attack the value of GI1 was changed on. For example, when GI1 = 0 on the third non-spell, Seiga shoots more knives at the player, or when GI1 = 0 on the first spell, Seiga will resurrect Yoshika.

Accessing the global variable GI1

In this stage, only Yoshika is able to write to GI1. On the other hand, Seiga reads GI1 and does certain actions depending on its value. The next section explains how GI1 is accessed on the second non-spell and second spell-card using ECL code.

Below the following subroutines are denoted:

• Boss2 being Seiga's second non-spell.
• BossMiyako2 being Yoshika, which is called right as Boss2 is called.
• BossMiyako2Dead being Yoshika's death subroutine, i.e. this gets called when Yoshika dies on the second non-spell
• BossCard2 being Seiga's second spell-card
• BossMiyakoCard2init being Yoshika, which is called right as Boss2 is called.
• BossMiyakoCard2 also being Yoshika, but this is called 160 frames after BossMiyakoCard2init is called. When called, GI1 is set to 1.
• BossMiyakoCard2Dead being Yoshika's death subroutine after BossMiyakoCard2 is called. When called, GI1 is set to 0.

To get more comfortable with these subroutines, some examples will be provided below with how the order of subroutines executed would look like in various scenarios.

Example 1 - Normal

Imagine you are fighting against Seiga and you are on her second non-spell and you do not kill Yoshika. Once the second spell starts, you stop shooting. The order of subroutines executed would be as follows:

Once BossMiyakoCard2 is called, the value of GI1 is set to 1. Below is a table that summarises the GI1 value per subroutine.

Example 2 - Normal

Imagine you are fighting against Seiga and you are on her second non-spell and you kill Yoshika. Once the second spell starts, you kill Yoshika two times. The order of subroutines executed would be as follows:

Once BossMiyakoCard2 is called, the value of GI1 is set to 1. When Yoshika dies, BossMiyakoCard2Dead is called, and the new value of GI1 is 0. Note that when Seiga revives Yoshika, Seiga calls for BossMiyakoCard2init. This subroutine then calls for BossMiyakoCard2, which continues the spell-card. In this example, reviving Yoshika is done twice.

Below is a table that summarises the GI1 value per subroutine.

Example 3 - Bugged

Imagine you are fighting against Seiga and you are on her second non-spell and you do not kill Yoshika. Once the second spell starts, you kill Yoshika within 160 frames of the spell starting. The order of subroutines executed would be as follows:

In this example, the subroutines BossMiyakoCard2 and BossMiyakoCard2Dead are never called because Yoshika was killed before they were able to be called. This means that Yoshika never writes to GI1, meaning the behaviour of Seiga depends on an earlier subroutine that set GI1.

Below is a table that summarises the GI1 value per subroutine.

For example, if the player ended spell-card 1 with Yoshika dead (so GI1 = 0), then Seiga will revive Yoshika in the earlier given example. However, if the player ended spell-card 1 with Yoshika alive (so GI1 = 1), then Seiga will not revive Yoshika.

Why this issue cannot happen elsewhere

While it may seem that more of Seiga's patterns could be affected, this is not the case.

Non-spell 1 & Non-spell 2

This non-spell does not read or write to GI1, so it never bugs out.

Non-spell 3

This non-spell does read and write to GI1. However, once the third non-spell Boss3 is called, Yoshika's subroutines are immediately called and her death subroutine is immediately overwritten meaning there is no window of time provided in which it is possible to achieve this bug.

Spell-card 3

Similarly, this spell has the same logic as spell-cards 1 and 2. However, the bug cannot be triggered on this spell because of the death call back on non-spell 3 (BossMiyako3Dead) setting GI1 to 0. This is unlike the death call backs of non-spell 1 and non-spell 2, which do not change the value of GI1.

Spell practice mode

This bug cannot happen on Spell practice mode. This is because when Yoshika is loaded first, she does not have a death call back. This behaviour means that she can have negative HP without her dying, meaning the spell-cards work as normal.

Conclusion

Links

Replays

• Replay Nylilsa by "Nylilsa". Lunatic, Youmu, 1.00c. 「February 11, 2025」. Download link (Note: Glitch showcase on Spell 2)

Videos

• TRDario. 「February 20, 2025」. "Yoshika respawn bug on spell 1 and 2" https://www.youtube.com/watch?v=9apV8MBpaok