SQL> with t as (
  2    select 'ABC' val from dual
  3    union all
  4    select 'Michel' from dual
  5    )
  6  select val, substr(val, column_value, 1) letter
  7  from t,
  8       TABLE(CAST(MULTISET(SELECT LEVEL FROM DUAL CONNECT BY LEVEL <= LENGTH(val))
  9                  AS SYS.odcivarchar2list))
 10  order by val, column_value
 11  /
VAL    L
------ -
ABC    A
ABC    B
ABC    C
Michel M
Michel i
Michel c
Michel h
Michel e
Michel l