Cython: Unable to cimport from `.pxd` file

I have a simple project directory and some simple files which failed to compile.

Directory structure:

cythonize: ROOT
|___ cythonize
    |___ __init__.pxd
    |___ __init__.py
    |___ first.pxd
    |___ first.pyx
    |___ second.pxd
    |___ second.pyx
|___ README.md
|___ setup.py

Let me show what are the exact content in every file.

__init__.pxd:

<EMPTY FILE>

__init__.py:

<EMPTY FILE>

first.pxd:

cdef class MyClass:
    cdef str good
    cdef str bad

    cdef str say(self, str x, str y)

first.pyx:

cdef class MyClass:

    cdef str say(self, str x, str y):
        return x

second.pxd:

from . cimport first # removing this does not help

second.pyx:

#cython language_level=3

from . cimport first

cdef first second(str a, str b):
    return first(a, b)

Objective

I am simply trying to cimport first from first.pxd into second.pyx in order to use first in second.pyx.

Compilation Errors

>>> cythonize -i -k -3 cythonize/second.pyx
Compiling C:\...\cythonize\cythonize\second.pyx because it changed.
[1/1] Cythonizing C:\...\cythonize\cythonize\second.pyx

Error compiling Cython file:
------------------------------------------------------------
...
#cython language_level=3

from . cimport first

cdef first second(str a, str b):
    ^
------------------------------------------------------------

cythonize\second.pyx:5:5: 'first' is not a type identifier

Error compiling Cython file:
------------------------------------------------------------
...
#cython language_level=3

from . cimport first

cdef first second(str a, str b):
    return first(a, b)          ^
------------------------------------------------------------

cythonize\second.pyx:6:11: 'first' is not a constant, variable or function identifier
Failed compilations: cythonize.second

Maybe one can show what is the minimum viable example that can make this work?