Custom tokenizer fails to encode despite characters being in mergeable_ranks about tiktoken HOT 1 OPEN

import tiktoken

cl100k_base = tiktoken.get_encoding("cl100k_base")
pat_str = cl100k_base._pat_str

tik_vocab = {'か'.encode(): 0, 'a'.encode(): 1}
tik_special_tokens = {}

enc = tiktoken.Encoding(
    name="tik_test",
    pat_str=pat_str,
    mergeable_ranks=tik_vocab,
    special_tokens=tik_special_tokens
)
print(enc.encode("aか"))