Heinkel Astrea/Relationships

Louanna Astrea
Heinkel loves his wife. In order to cure his wife, Heinkel was prepared to do anything, even if it meant going out of his way to the Barielle Territory and slaughter an entire camp of bandits, as he had heard rumours of a meteor which can heal any illness, if a person drinks from it (though the cup turned out to be a fake, and was only capable of turning alcohol into a drug that numbs the pain). He even verbally abuses Garitch Fabless for not being able to heal her. He later admits that his wife is unable to be healed and buries his sorrow in alcohol.

Reinhard van Astrea
Heinkel dislikes Reinhard, as he thinks that Reinhard is the reason behind his family's situation.

15 years before the start of the main story, however, Heinkel well and truly loved Reinhard, to the point he was prepared to do anything and everything, to have his son by his side. He never got angry at him and treated him as his and Louanna's treasure.

Priscilla Barielle
Priscilla encountered Heinkel some time between Arcs 5 and 6, when Heinkel slaughtered an entire camp full of bandits, in order to retrieve the aforementioned Meteor which was said to have magical properties and could heal any illness one had, just by drinking for it (naturally, the cup did not hold such magical properties, but rather, was capable of turning any beverage into a drug that numbs all the pain). As Priscilla was about to kill him, Heinkel suggested she should accept him into her Camp, as he knew of a way to dispose of his son's mistress. In return, he wanted the Dragon's Blood, which would surely bring Louanna back to life.

Following that day, Heinkel joined Priscilla Camp and started acting as another one of Priscilla's swords.

Al
Al and Heinkel mutually respect each other (at least somewhat), and Al even complimented Heinkel's skill with the sword.

Al also usually takes Schult's side, when Heinkel showers the young boy with insults.

Schult
Heinkel can be seen caring about Schult, perhaps even considering him something close to a son–a son without any special powers. Though, despite that, he's overly harsh with him, to the point Priscilla had to threaten Heinkel to stop, otherwise she'd lob his head off.

Marcos Gildark
Fifteen years before the main story, Marcos and Heinkel were very good friends. Following Marcos' resignation from the Royal Army due to his dissatisfaction with the work he had to do (lock up innocent people from the slums, rather than help them get their lives back on their feet), Heinkel repeatedly went to visit him, trying to convince him to rejoin the Royal Army. This eventually resulted in young Reinhard–who wanted to help his father out in any way possible–to wish and gain the Divine Protection of Mind Manipulation and manipulate Marcos to rejoin the ranks of the Kingdom's Knights.

It's unknown how Heinkel's and Marcos' relationship continued, after that event.