[ʃ] are in complementary distribution within Japanese as I already know, but I don't speak Japanese and I'm finding it difficult to give examples how they are in distribution, are there any examples which could work?
As has been noted in the comments, [s] and [ɕ] (sometimes broadly transcribed as [ʃ]) are not in complementary distribution in Japanese. However, they can be analyzed as allophones of the same phoneme.
The following rule can be used to explain some of the facts:
/s/ --> [ɕ] before [i], [s] elsewhere
[asa] 'morning' [ɕi] 'four' [aɕi] 'foot' [isu] 'chair' [seki] 'cough' [heso] 'belly button'
However, [ɕ] also appears before other vowels besides [i]:
[iɕa] 'doctor' [hoɴɕuː] 'Honshu' [ɕoːyu] 'soy sauce'
This leads to an analysis in which it is sensible to treat /ɕ/ as its own phoneme.
Not counting the less nativized loanword pronunciations of words (like [siː] for the English letter 'C'), we never get [s] before [i]. Related forms like [osu] 'press-PRESENT' and [oɕita] 'press-PAST' give us further evidence that at least some instances of [ɕ] before [i] are likely surface realizations of /s/.
So, one analysis that captures all of the facts is that there are two phonemes--/s/, which has the allophones [s] and [ɕ], and /ɕ/, which always surfaces as [ɕ].
EDIT: In response to comments below, here is an alternative analysis that can also capture the facts:
We observe that palatalized versions of consonants may appear before [a], [o], and [u]:
[kʲoku] 'piece of music' [nʲuːiɴ] 'hospitalization' [ɾʲoːhoː] 'both' [hʲaku] 'one hundred' [happʲaku] 'eight hundred' [sambʲaku] 'three hundred' [bimʲoː] 'subtle'
(The choice of transcription of these Cʲ onsets varies; some choose to use [ç] instead of [hʲ], for example.)
There are some gaps--the alveolar stops ([t], [d]), alveolar fricatives ([s], and [z]), and the bilabial approximant [w] do not have palatalized counterparts. The [w] gap is not an unexpected one, since [w] is the only approximant (besides [j] itself). Historically, the palatalized counterparts of [t], [d], [s], and [z] became what are now the alveolo-palatal consonants [tɕ], [dʑ], [ɕ], and [ʑ], respectively. Further, these alveolo-palatal consonants do not have palatalized counterparts (there is no [ɕ]/[ɕʲ] contrast, for example).
Due to the above facts, some consider it reasonable to adopt a synchronic analysis in which all surface occurrences of [tɕ] and [dʑ] are underlyingly /tʲ/ and /dʲ/, respectively, and all surface occurrences of [ɕ] and [ʑ] are underlyingly /sʲ/ and /tʲ/ (or even /sj/ and /tj/), respectively.