Chrivi writes the affricate ch and carries no numeral value in Glagolitic, standing beyond the end of the counted series. Like the other letters in this stretch it exists for a Slavic sound that Greek had no sign for.
The affricate is another product of the softening of an original velar, and it stands in a regular relationship with the plain velar stop earlier in the alphabet. The same root will show the stop in one form and this affricate in another, and that alternation runs through the whole of Slavic to the present day, so a modern speaker of any Slavic language uses it without thinking about it.
The name is opaque. The reference works record it without a gloss, and the atlas carries an open question about the whole set of names at this end of the alphabet rather than proposing an etymology for any one of them.
In the manuscripts the letter is common enough to be well attested in both the rounded and the angular hands. It is one of the signs where the two hands differ enough that a reader has to learn the form twice, which is true of a good many letters in the second half of the alphabet where the shapes are more elaborate than the plain Greek-answering signs at the start.
Its position in the order is one of the details on which the sources are not quite uniform. The letters for the affricates and the sibilants are listed in slightly different sequences by different abecedaria, and the atlas follows the arrangement of the Unicode Standard, which is a decision among attested possibilities rather than a reading of a single authoritative list.