case of “The EU Blue Card” holder

21 months after working in Germany, I got a German settlement permit.
Here I would like to introduce requirements for applying settlement permit in Germany as a holder of “The EU Blue Card / Blaue Karte EU”. (Oct. 2019)
Disclaimer:
Please be advised that this page cannot guarantee, in any way whatsoever, the validity of the information found here. Use at your own risk.
Incidentally, the author of this page is Japanese (“citizens of third countries”) . If you prefer reading in Japanese, here is the link.
Residence in Germany
If you are a citizen of a “third country” and would like to remain in Germany, you therefore need a permit, the “residence title”:

1.Residence permit
2.EU Blue Card
3.Permanent settlement permit
4.EU long-term residence permit
(BAMF)
In short, type 1 and 2 are limited permit, type 2 is for highly qualified workers, type 3 and 4 are unlimited, type 4 also entitles the holder to mobility within the European Union by granting a right to a limited residence title in the other Member States.
The residence permit is issued for a limited period of time.
It is granted to persons who・ would like to undergo training in Germany
・ would like to work in Germany
・ are entitled to remain in Germany for humanitarian or political reasons or under international law
・ are immigrating to Germany for family reasons
・ are foreign nationals and former Germans who would like to return to Germany , or
・ hold a permanent right of residence in another Member State of the EU
(Sourse: BAMF.de)
What is “The EU Blue Card / Blaue Karte EU”?

On 1st August 2012, the EU Blue Card was introduced as a new residence title. It is issued to foreign workers for them to pursue a highly-qualified occupation, provided that the salary received for this occupation is at least equal to a statutory minimum salary.
(Sourse: EU Blue Card — Berlin.de)
In short, if you have a university degree you can apply for an EU Blue Card to enable you to work in Germany and EU countries. A certain minimum salary is necessary for this.
It might also be noted, if you are “Freelancer” or “Self-employed”, you cannot apply for the EU Blue Card.
Requirements for applying The EU Blue Card
Prerequisites — EU Blue Card
-Specific university degree
-Employment
-Minimum salary*
shortage occupation: EUR 3,484 gross /month (EUR 41,808 / year)
another profession : EUR 4,467 gross /month (EUR 53,600 /year)
Shortage occupations : scientists in natural science disciplines, mathematicians, architects, interior, urban and traffic planners, designers, engineers, scientific engineers, physicians (except dentists) and those with academic qualifications in information and communications technology.

Documents required for The EU Blue Card (Source:Berlin.de)
-Form “Antrag auf Erteilung eines Aufenthaltstitels”
-For the approval of the Federal Employment Agency: additional forms
-Your passport
-Proof of your residence
-Current biometric photo
-University or university college qualification (Original)
-If necessary: Zeugnisbewertung
-Your employment contract or job offer (Original)
-If necessary: Occupation practice permit
-Proof of your health insuranceWhat is “the settlement permit / Niederlassungserlaubnis”
What is the settlement permit — Niederlassungserlaubnis?

Literally, with this settlement permit, you are allowed to stay in Germany indefinitely.
As a supplemental explanation, “settlement permit / Niederlassungserlaubnis” in the current law “Aufenthaltsgesetz” is, strictly speaking, different from “permanent residency / Aufenthaltsberechtigung” in the former low “Ausländergesetz”. Therefore, in this page I’d like to use “settlement permit / Niederlassungserlaubnis” for this naming .
Who can apply for “Settlement Permit” ?
Issue of a permanent settlement permit in accordance with different legal bases.
The following cases of residence are subject to different requirements:・ persons recognised as being entitled to asylum and refugees
・ foreign graduates of German universities
・ family members of German nationals
・ EU Blue Card holders
・ children (older than 16)
・ self-employed persons
(Berlin.de)
(In my case, I applied in Düsseldorf, but I recommend to check the website of Berlin, which has more detailed explanations.)
Settlement permit for The EU Blue Card holders
Prerequisites Comparisons of for Settlement Permit
— General / EU Blue Card holder

Large difference between general applicant and EU Blue Card holder is:
EU Blue Card holder can shorten the possession of a residence together with payment of pension from 60 months to 21 months with sufficient knowledge of German B1 Level (33 months with A1 Level).
-Application in writing
-Sufficient knowledge of German (level B1/A1 of the CEFR)
-Possession of a residence permit for 5 years / 33/21 months
-Payment for German Pension Fund at least 60 /33/21 months
-Knowledge of the legal and social system and living conditions in Germany
-Secured means of support from own income
-Sufficient health insurance
-No criminal record
-Main residence in the city of Germany
-Fee 113.00 euros
(Berlin.de)
Besides EU Blue Card, there are similar exceptions for required possession of a residence permit and payment of pension for settlement permit :
- foreign graduates of German universities — 2 years
- family members of German nationals, you can shorten — 3 years

I hope this overview is helpful for people who has similar situation as I had or who is planning to move to Germany or who has interest working in Europe.
REFERENCES
BMMF
Aufenthalt in Deutschland — BMMF Bundesamt für Migration und Flüchtlinge
The EU Blue Card — Federal Office for Migration and Refugees
Aufenthaltsgesetz — AufenthG
Aufenthaltsgesetz — § 18 Beschäftigung
Aufenthaltsgesetz — § 19a Blaue Karte EU
Aufenthaltsgesetz — § 9 Niederlassungserlaubnis
Aufenthaltsgesetz — § 9a Erlaubnis zum Daueraufenthalt — EU
Berlin.de
Employment / foreign workers — Berlin.de
EU Blue Card- Berlin.de
Permanent residence titles — Berlin.de
Permanent settlement permit for EU Blue Card holders- Berlin.de
Düsseldorf.de
Niederlassungserlaubnis (unbefristete Aufenthaltstitel)
