<s>
is	O
a	O
bullet	O
hell	O
platform	O
game	O
numbered	O
as	O
the	O
17.5th	O
in	O
the	O
Touhou	B-Application
Project	I-Application
series	O
.	O
</s>
<s>
Sunken	O
Fossil	O
World	O
is	O
the	O
first	O
Touhou	B-Application
spinoff	O
by	O
Twilight	O
Frontier	O
which	O
is	O
not	O
a	O
fighting	O
game	O
.	O
</s>
<s>
Like	O
all	O
previous	O
Touhou	B-Application
Project	I-Application
spinoffs	O
where	O
Twilight	O
Frontier	O
were	O
involved	O
,	O
ZUN	O
of	O
Team	O
Shanghai	O
Alice	O
only	O
oversaw	O
the	O
development	O
of	O
the	O
game	O
and	O
scenario	O
,	O
while	O
Twilight	O
Frontier	O
actually	O
developed	O
the	O
game	O
.	O
</s>
<s>
The	O
game	O
was	O
supposed	O
to	O
release	O
at	O
Touhou	B-Application
's	O
Reitaisai	O
18	O
convention	O
on	O
March	O
21	O
,	O
2021	O
,	O
but	O
it	O
was	O
announced	O
that	O
the	O
game	O
would	O
be	O
further	O
delayed	O
,	O
due	O
to	O
parts	O
of	O
the	O
game	O
still	O
being	O
completely	O
missing	O
.	O
</s>
<s>
Because	O
of	O
delays	O
,	O
the	O
game	O
presents	O
a	O
subtitle	O
of	O
"	O
17.5	O
"	O
,	O
despite	O
being	O
released	O
after	O
the	O
18th	O
Touhou	B-Application
game	O
,	O
Unconnected	B-Application
Marketeers	I-Application
.	O
</s>
<s>
A	O
Nintendo	B-Application
Switch	I-Application
port	O
as	O
well	O
as	O
an	O
update	O
featuring	O
new	O
playable	O
characters	O
and	O
storylines	O
was	O
announced	O
in	O
May	O
2022	O
.	O
</s>
