search_word = '大谷翔平'

from docx import Document
from docx.shared import RGBColor


doc = Document('/Users/mac/Documents/ottani.docx')
search_word = '大谷翔平'

for paragraph in doc.paragraphs:
    if search_word in paragraph.text:
        for run in paragraph.runs:
            print('1',run.text)
            if search_word in run.text:
                new_run = paragraph.add_run(run.text)
                for i, char in enumerate(run.text):
                    if char == search_word[0] and run.text[i:i + len(search_word)] == search_word:
                        new_run.font.color.rgb = RGBColor(255, 255, 0)  # Yellow color
                        new_run.text = new_run.text[:i] + search_word + new_run.text[i + len(search_word):]
                        paragraph.runs.remove(run)
                        break

doc.save('/Users/mac/Documents/ottani_mark.docx')