Japan's first and only European born Diet member Marutei Tsurunen.Can someone kindly explain why romanization of his surname became Tsurunen not remained as actual spelling Turunen ? Why in Japanese,you need to add the " s " ?
There is no 'actual' way of spelling a Japanese word using Roman characters, transliterations are there merely as a convenience for foreigners. Several systems exist, of which Hepburn is the most commonly used, but it's not uncommon to see ti, tu etc rather than chi, tsu. I seem to recall it was used in some of the textbooks I used in Japanese schools.
No foreign characters are allowed to make registration of Japanese national. Hence, foreign names must be transcribed in Japanese characters, using kana and kanji.
As far as the naturalized ex-Lutheran missionary chose his name to be Japanized enough, it is not strange that he would have taken "つ tsu" instead of "とぅ tu” for his Japanese name.
I guess what he chose is not a transliteration of his Finnish name, written in Hepburn romanization.
He took up a Japanese name, based on his original Finnish name.
Because his "official name" which is duly shown on his "japanese passport" (as he is now a Japanese national) is written according to his resident registration filed at the local authories in **Japanese language**, his name in romanization is subsequently an exact representation of his Japanese name in Japanese phonological rules --- not とぅ、but つ。