This paper focuses on the verbal inflection chain of Siyuewu Khroskyabs, a Gyalrongic language (Trans-Himalayan). Siyuewu Khroskyabs goes against two general typological tendencies: first, as an SOV language, it shows an overwhelming preference for prefixes, which is rarely reported typologically; second, the inflectional prefixes in the outer slots are older than those in the inner slots, which is the reverse case of most languages. In this paper, I will first identify distinct historical layers within the inflectional prefixes, and then focus on two of the prefixes, də- ‘even’ and ɕə- ‘q’ whose evolutionary pathways are relatively clear. The essential part of the hypotheses is that the prefixes originate from enclitics which could be attached to the end of a preverbal chain, originally loosely attached to the verb stem. The preverbal chain later became tightly attached to the verbal stem and eventually became a part of it as a chain of prefixes. As a result, the original enclitics are reanalysed as prefixes. The integration of preverbal morphemes is responsible for the prefixing preference in Modern Siyuewu Khroskyabs. However, despite this superficial prefixing preference, Siyuewu Khroskyabs underlyingly favours postposed morphemes. By following the general suffixing tendency, this language finally managed to create a typologically rare, overwhelmingly prefixing verbal template.