Baidu user 白龙圣骑士SK wrote a compelling theory on the lineage of Rean Schwarzer. It’s a schoolbook example of a theory, thought-provoking and built on in-game evidence.

I. Fateful encounter in a remote region

As [Osborne] was stationed at a garrison in a remote region at the age of 35, he had a fateful encounter with a certain girl.

– Olaf Craig (Chapter 4, Sen III)

Poster argues that the garrison Brigadier-General Osborne was stationed at was the Dreknor Fortress in Sutherland Province. The background in the flashback surely resembles the actual in-game fortress. For comparison:

Geographically Dreknor Fortress is situated in the next to Isthmia Great Forest, home of Erin Village, the Hexen Clan hometown. Running into a witch or two while working so close nearby their hometown is certainly not unthinkable.

I myself would like to add that the first two Cold Steel also continuously refer to Emma’s hometown as a remote region, e.g.:

• Summary of Emma’s introduction in the notebook (CS1): “We were introduced to Emma, who scored highest on the entrance exam, and came from a remote region of the Empire.”
• Emma’s character note (CS1): “Intelligent, broad-minded girl who came from a remote region of the Empire”.
• Summary in Cold Steel II: “Class VII’s class president, and a girl who came from a remote region of Erebonia to attend Thors on a scholarship.”

II. The witch between the lines

Emma’s mother was a “deserting witch”. She went on to live among the common people and lost her life in an unfortunate accident.

– Celine

At the age of 16, Vita volunteered as “wandering witch”.

– Celine

[Emma] somehow gained the support of a deserted witch. She took Thors’s entrance exam and got the scholarship.

– Celine

Since Vita qualifies as “wandering witch”, Emma got into Thors with the help of a yet unmentioned witch.

Vita lost her parents on a young age. She was expected to show great potential so the elder [Roselia] took her in as her foremost disciple.

– Celine

Furthermore, Celine also reveals the role of not just Vita, but of every “wandering witch”:

To get a clear view of the state of the world outside the village.

– Celine

In other words, the role of “wandering witch” is the only way to observe the outside world without giving up the rest of the clan like a “deserting witch”. In conclusion, poster argues, this suggests that Roselia was raising Vita as her successor.

Vita left the village, carrying with her a staff from Roselia (which we have discussed in length before). The staff was probably useful for Vita’s plans.  Upon seeing Roselia with her staff in Sen III, Rean immediately remarks it’s the same as Vita’s but with a different colour. After the events of Cold Steel II, Vita returned the staff to Roselia.

(The staff’s colour is determined by its wielder: red with Roselia, blue with Vita and purple with Emma)

[When Vita teamed up with Ouroboros] the elder deeply regretted she hadn’t been more careful since something similar happened in the past.

– Celine

This suggests there used to be another successor for Roselia before Vita, poster stresses.

The question remains whether Kasia, the hitherto unmentioned witch, had her fateful encounter with Osborne before she deserted the village or deserted the village because she met with him in the forest?

III. Born to be magic resistant

Although not a witch, that one night in chapter 3 of Sen III, Musse Egret uses actual magic she had learnt to allure Rean, but alas:

Oops, it failed. One of the people I hold in high esteem taught me this magic to captivate gentlemen.

– Musse

It is not the first time we’ve seen this happen. Vita, dressed up as Misty, did something similar.

Both Vita and Crow knew that Rean was selected as the Awakener of Valimar (unlike Emma in the beginning), so it would’ve been impossible for Vita to be genuinely surprised at Rean’s identity as Awakener.

I had this feeling I’d seen you before, but I couldn’t put my finger on where. ……But it’s ‘you,’ isn’t it?

-Misty

In Sen no Kiseki III, both Teo Schwarzer and Olaf Craig point out that Rean looks like his mother. Teo could tell Rean was Osborne’s son at a glance because he closely resembled Osborne’s wife.

Hmhm. You have your father’s hair and your mother’s face.

– Olaf Craig

In conclusion, Vita’s suspicions were aroused by Rean’s ability to break her spell. Then she noticed the familiarity of Rean’s facial features. Vita quickly put the two together, realising that the magic resistant-born Rean is the son of the wandering witch who deserted the Hexen Clan village, Kasia Osborne.

Two other things Kondo pointed out: (1) only those with the adaptability of a witch are able to detect/locate the Hexen Clan village, and (2) although still referred to as witches, there might be males living in the village.

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IV. Uncertainties surrounding the attack on Osborne’s home

Further down the thread, posters shares another related and equally interesting observation. Apart from highlighting the dubious motives to attack Osborne’s home knowing he wasn’t home to begin with, poster also points out Olaf Craig’s uncertainty in his story about the raid on Osborne’s home.

The brigadier-general’s home on the outskirts of Heimdallr was attacked by a jaeger-like group.

It seemed as if the fire had been lit late at night that set the brigadier-general rushing back home.

What was found the following morning was the burnt-down house, the corpses as if the brigadier-general turned the tables on them and the remains of his wife.

The Brigadier-General, who apparently lost a great amount of blood, and his 5-year-old son were nowhere to be found.

– Olaf Craig

Also, poster concluded his post, did Osborne lose the blood fighting his attackers or did he transplant his heart into Rean on the spot?