Christian existentialism is a theo-philosophical movement which takes an existentialist approach to Christian theology.
 The school of thought is often traced back to the work of the Danish philosopher and theologian Søren Kierkegaard (1813–1855), who some consider the father of existentialism.
Søren Kierkegaard's theology has been a major influence in the development of 20th century theology.
 Søren Kierkegaard (1813–1855) was a 19th-century Danish philosopher who has been generally considered the "Father of Existentialism".
 During his later years (1848–1855), most of his writings shifted from being philosophical in nature to being religious.
"Atheistic existentialism" is a kind of existentialism which strongly diverged from the Christian existential works of Søren Kierkegaard and developed within the context of an atheistic world view.
 The philosophies of Søren Kierkegaard and Friedrich Nietzsche provided existentialism's theoretical foundation in the 19th century, although their differing views on religion proved essential to the development of alternate types of existentialism.
 Atheistic existentialism was formally recognized after the 1943 publication of "Being and Nothingness" by Jean-Paul Sartre, and Sartre later explicitly alluded to it in "Existentialism is a Humanism" in 1946.
Existentialism and Humanism (French: "L'existentialisme est un humanisme" , "Existentialism is a Humanism") is a 1946 work by the philosopher Jean-Paul Sartre, based on a lecture called "Existentialism is a Humanism" he gave at Club Maintenant in Paris, on 29 October 1945.
 "Existentialism and Humanism" was the title used in the United Kingdom; the work was originally published in the United States as Existentialism.
 The work, once a popular starting-point in discussions of Existentialist thought, has been criticized by several philosophers.
 Sartre himself later rejected some of the views he expressed in it and regretted its publication.
Sickness Unto Death (Japanese: 死に至る病 , Hepburn: Shi ni Itaru Yamai ) is a Japanese manga series written by Hikaru Asada and illustrated by Takahiro Seguchi.
 A two-volume compilation by Hakusensha was published on February 26, 2010.
 Vertical published the manga in the United States, releasing volume 1 on September 24 and volume 2 on November 19, 2013.
 The manga's title is taken from Søren Kierkegaard's book "The Sickness Unto Death", which the character of Kazuma utilizes at various points throughout the manga.
Søren Kierkegaard's philosophy has been a major influence in the development of 20th-century philosophy, especially existentialism and postmodernism.
 Kierkegaard was a 19th-century Danish philosopher who has been called the "Father of Existentialism".
 His philosophy also influenced the development of existential psychology.
Søren Aabye Kierkegaard ( or ; ] ; 5 May 1813 – 11 November 1855) was a Danish philosopher, theologian, poet, social critic and religious author who is widely considered to be the first existentialist philosopher.
 He wrote critical texts on organized religion, Christendom, morality, ethics, psychology, and the philosophy of religion, displaying a fondness for metaphor, irony and parables. Much of his philosophical work deals with the issues of how one lives as a "single individual", giving priority to concrete human reality over abstract thinking and highlighting the importance of personal choice and commitment.
 He was against literary critics who defined idealist intellectuals and philosophers of his time, and thought that Swedenborg, Hegel, Goethe, Fichte, Schelling, Schlegel and Hans Christian Andersen were all "understood" far too quickly by "scholars".
Ferdinand Ebner (January 31, 1882 in Wiener Neustadt – October 17, 1931 in Gablitz, Austria), was an Austrian elementary school teacher and philosopher.
 Together with Martin Buber and Franz Rosenzweig, he is considered one of the most outstanding representatives of dialogical thinking.
 Ebner's philosophy is about man existing in a I-Thou personal relationship with God and with others.
 His thought has similarities with the Christian existentialism of Gabriel Marcel.
 On the basis of the unity of I and Thou, which has in language (in the spoken word), and in love its expressions, Ebner developed a religiously informed philosophy of language which led to his practical-ethical understanding of the Christian faith as the basis for the personal fulfillment and the whole social progress.
Christian existential apologetics differs from traditional approaches to Christian apologetics by basing arguments for Christian theism on the satisfaction of existential needs rather than on strictly logical or evidential arguments.
 Christian existential apologetics may also be distinguished from Christian existentialism and from experiential apologetics.
 The former is a philosophic outlook concerned with the human condition in general; the latter consists of evidential argumentation based on religious experience.
The Sickness Unto Death (Danish: "Sygdommen til Døden" ) is a book written by Danish philosopher Søren Kierkegaard in 1849 under the pseudonym Anti-Climacus.
 A work of Christian existentialism, the book is about Kierkegaard's concept of despair, which he equates with the Christian concept of sin, particularly original sin.

Question: What book on Christian existentialism is by what Danish philosopher?
Answer: Søren Kierkegaard