echo-from-the-void:

Hairu had a huge desire that she would be praised by the CCG`s Reaper, Arima Kishou, one day. We know that Arima hardly praises anyone, so this seems like an impossible task. But what if our First Class investigator thought she had found a way? Maybe by becoming more like Arima? If my memory serves me correctly, Hairu already demonstrated she is capable of doing the Arima dodge, so she surely is a very capable fighter. But what if she also wanted to copy Arima`s weapons?

I was reading around the TG wiki a few weeks back, and noticed that in Hairu`s page it reads that she had interest towards Arima`s quinque, IXA. Later during the Tsukiyama extermination mission when the investigators face Shuu`s knight, Matsumae, Hairu shows interest towards Matsumae`s kagune. This might just be a normal investigators cold calculating mind in the works, but what if she also saw Matsumae`s weapons as a potential new IXA? IXA is an koukaku type weapon, looking like a lance, but also capable of forming an defensive mode

Offensive IXA 

Defensive mode:

Now, lets look at Matsumae`s kagune, which is koukaku like IXA:

Yup, a lance and shield. If I was looking to have a new IXA, that is a kagune I would choose. 

Since Hairu already has something that resembles very much to Arimas`s Narakumi qunique, T-Human, an IXA copy is all she needs to become an Arima copy.By becoming a copy maybe she thought the Reaper would finally praise her?

Well, those were my thoughts. This is probably just me overthinking this and even if this was correct, it is a rather small detail in the grand scale of things. Sadly both Matsumae and Hairu are also gone. T-T